Biodiversity Net Gain

The Experts Guide to Biodiversity Net Gain

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Biodiversity Net Gain (BNG)

Biodiversity Net Gain (BNG) is a mandatory principle that has been implemented into all development plans within the UK. In the realm of environmental planning, this essentially lays out a list of actions to take during the development that would not only save the natural elements of the area but leave them better off than before. 

BNG’s importance cannot be overstated. Biodiversity offers a range of ecological functions, such as pollination, soil stabilisation and climate regulation. All three of these things not only benefit nature but also human health and well-being. BNG essentially offers greener, healthier spaces to live and work. Local wildlife populations are also enhanced, and over time, nature will improve globally. 

With Indigo Surveys, we conduct biodiversity net gain projects to enable businesses and developers to exceed their BNG obligations. We do this through an efficient, effective process that cuts down on all possibilities for delays. With us, these strict regulatory requirements will become opportunities for communal, environmental growth and harmony. Our services range from the initial biodiversity impact assessment to the development of habitat creation, plans for long-term management and stakeholder engagement. 

With our expertise, we ensure our clients meet their Biodiversity Net Gain needs. 

About Biodiversity Net Gain

BNG is a concept that is transformative in the environmental planning scene. It obligates all developers to ensure that their projects not only aren’t taking away from the environment, but also enhances it. The gain is determined using the Defra Biodiversity Metric. 

Defra Biodiversity Metric

The Defra Biodiversity Metric measures both the pre and post-development biodiversity value of the development site. It essentially breaks the site down and calculates the “biodiversity units”. 

The biodiversity units are calculated based on habitat distinctiveness, habitat condition and the size of the area. After evaluating all of these factors, they are given a score and then combined into biodiversity units. This serves as a baseline measurement before development takes place. 

Of course, after the development, the same metric is used to determine the new biodiversity value of the site. The goal is to ensure that the post-development value is at least 10% higher than the baseline measurement. 

This metric is crucial in its provision of a standardised, objective and transparent means of quantifying biodiversity. It’s a basic way for developers, planners and local authorities to understand and make plans surrounding the ecological power of your site. 

What’s the point? 

The point is, largely, to understand that regular practices in development mostly take away from the ecological power of the UK. As such, BNG practices are put in place to safeguard existing habitats and push toward enhancing and creating new ones. This could result in the recovery of declining wildlife populations, which have been declining rapidly since the industrialisation era of the UK. 

BNG is a complex process requiring careful planning, execution and monitoring. Each stage of the development process – from site selection, to design and construction, to long-term management – must have these considerations built-in, or there’s a risk your development proposal may be dismissed. 

At Indigo Surveys, we strive to ensure that your surveys will happen with the utmost streamlined procedures. We will turn your development project into a catalyst for environmental change.


biodiversity net gain

Indigo Survey’s Biodiversity Net Gain – Step by Step

Upon contacting us, we will do the following. 

Preliminary Ecological Appraisal

This is also known as a Phase 1 habitat survey

The purpose of this survey is to discover and catalogue the ecological features that are present within and around a site of development that are protected by the government. The steps of a PEA are: 

  • Desk Study – This is a review of all existing information of the area – such as wildlife records, designated sites, geological maps and aerial photographs. 
  • Site Visit – Our specialists will physically enter the zone to carry out a field survey, which consists of mapping out the different habitat types on site. In particular, there will be an intention to note signs of protected species and evaluate the potential impacts of the proposed development. 
  • Species Survey – If there is an identifiable chance that there are protected species on site, then our ecologist will also carry out a targeted species survey. Some of these species could be bats, newts and badgers, for example. 
  • Impact Assessment – This part of the PEA will identify what impacts your development may have on the site, such as the noise levels it may add. 
  • Recommendations – To ensure your development goes as smoothly and fast as possible, Indigo Surveys will give you recommendations on avoiding, minimising or mitigating any potential impacts. These can range from creating new habitats for the species, or changes to development design. 

Biodiversity Impact Assessment 

This is the phase where a quantification will be made on the existing biodiversity of the site. This will establish a baseline to measure the target net gain your project must achieve using the Defra Biodiversity Metric. 

The process is as follows: 

  • Habitat Classification – The first step in BIA is using the Defra Metric to classify the habitats present on site. For example, grassland, woodland, rivers and ponds. 
  • Habitat Condition – The condition of each area catalogued will also be graded for its condition. For example, vegetation structure, species diversity and evidence of negative pressures such as pollution or an invasive species will be scored in one of four grades. These grades are “poor”, “moderate”, “good”, and “excellent”. 
  • Size and Location – The area of each habitat is measured and graded based on its size and physical connection to other habitats within and around the development site. The more well-connected and significant a habitat, the higher its value. 
  • Calculating Biodiversity Units – All these factors are combined to calculate the total biodiversity units for the site. The way this is done is by multiplying the base biodiversity value of each habitat by the condition, size and location score. 


This information is then used to formulate a plan on how to take the biodiversity value, and have it increase by 10% after the development is finished. 

BNG Strategy Development 

The results of the previous phase will be used to develop a plan for the Biodiversity Impact Assessment.

These are the steps involved in the BNG Strategy Development:

  • Impact Identification – Development Plans will be analysed in detail, taking into consideration what impacts they may have on the biodiversity score. 
  • Avoidance Measures – Avoidance measures proposed could be anything from modifying the development layout/location to avoid high-value habitats, or timing the works to avoid vulnerable periods for wildlife. 
  • Minimisation Measures – If impacts cannot be avoided, then it falls to us to look for ways to minimise any damages that happen as a result. For example, implementing features to your site to allow wildlife to move through it without obstruction. 
  • Mitigation Measures – Any remaining impacts should be mitigated, meaning the improvement of the conditions of existing habitats, or the creation of new ones. 
  • Enhancement Opportunities – Identifying opportunities to enhance biodiversity is probably the most important step in the entire process. This does a lot of the heavy lifting in reaching the extra 10% biodiversity you need. 
  • Long-Term Management – The long-term management of the site to ensure that the gains in biodiversity from the enhancement are maintained over time, such as monitoring and managing the habitats in question. 

Habitat Design and Creation 

The previous phase’s results are collected and put into a plan, creating a strategy to put the habitats agreed upon into action. 

  • Planning – Drawing on the findings of the last two phases, the planning stage involves identifying the most effective ways to enhance existing habitats or create new ones. For example, this could be identifying and choosing the best location for a new habitat. 
  • Implementation – This stage is simply putting the plans you’ve made into action. This may involve building ponds or wetlands, or planting trees and vegetation. 
  • Monitoring and Adjustment – After these habitats have been created, you now have to put a protocol in place to ensure that they are properly monitored, with an eye for ensuring that the development maintains its 10%+ biodiversity goal. If not, adjustments can be made to ensure that it does. 


This is the stage where the theoretical practices written down during the BNG Strategy Development are implemented. 

  • Staged Work – You will take the schedule of everything that needs to be done, and break it up into stages. The benefit of this is simple, you can manage the workload you’re putting in by splitting it into chunks, ensuring that whilst these specific tasks are done, the wildlife are not being harmed. Heavy construction could interrupt birds during spring, for example, so it’s advisable to do another task during that stage. 
  • Implementation of Mitigation Measures – The measures drawn up during the BNG strategy, derived from what was identified during the BIA phase, is implemented during this phase. This could include installing protective fences, or safely relocating wildlife. 
  • Habitat Creation and Enhancement – Any habitats that were planned to be created or enhanced during the previous Habitat Design and Creation phase. For example, tree planting and pond creation. 
  • Monitoring of Work – Regular monitoring will be conducted throughout the phase to ensure that works are all carried out in accordance with the BNG Strategy and that all mitigation measures are effective. 

Post-Construction Assessment

After the development has been fully finished, it’s time for our experienced specialists to come back to do another survey. It will be exactly like the preliminary ecological assessment, only this time the goal is to see what changes have happened as a result of the development. Biodiversity units will be measured again and compared with the results taken during the first phase. 

What if you don’t meet the Biodiversity Target? 

Depending on the actual results, this could cause rather large issues. Biodiversity Net Gain targets are generally a legal requirement in the UK to meet when assigned. But it doesn’t mean that you’re necessarily in legal trouble, especially if you followed the plans laid out. Unseen circumstances happen, after all. 

To fix not meeting your net gain target, the issue will be revisited in the form of additional plans to improve Biodiversity Units. For example, the further creation of habitats worth a higher level of Biodiversity Units. 

Should this also fail, or should there be no way to increase the units in this manner, then off-site biodiversity offsetting may be required. This involves increasing the biodiversity score of habitats in another location to compensate for the loss on the development site. It’s worth pointing out that this is not preferred, however, as whilst you’re giving back to the environment, you’re still taking away from the development site. 

How does BNG help to achieve the goals of the UK’s 25-Year Environment Plan?

The UK’s 25-Year Environment Plan, unveiled by the government in 2018, sets out a comprehensive and long-term approach to protecting and enhancing the country’s natural landscapes and habitats for the next generation. 

The plan includes goals that span across clean air, clean and plentiful water, thriving plants and wildlife, reduction of pollution, efficient use of resources, minimisation of waste, and mitigation of climate change, amongst others.

Biodiversity Net Gain (BNG) plays an integral role in realising many of these objectives.

Here’s how:

  1. Thriving plants and wildlife: BNG explicitly aims to increase biodiversity, helping to create more habitats for native species to flourish. By measuring and ensuring an increase in biodiversity value after development, we promote healthier ecosystems.
  2. Clean and plentiful water: BNG often involves the creation or enhancement of wetland habitats which can improve water quality, reduce flood risk, and provide a habitat for aquatic species.
  3. Clean air: Enhanced green spaces as part of BNG can contribute to better air quality by absorbing pollutants and releasing oxygen. This is especially beneficial in urban areas.
  4. Climate change mitigation: Healthy, biodiverse ecosystems play a crucial role in sequestering carbon, hence aiding in climate change mitigation efforts. Additionally, BNG initiatives often involve planting trees or improving forests, both critical for carbon storage.
  5. Connection with nature: By creating richer, biodiverse spaces, BNG can also contribute to the plan’s goal of connecting people with the environment to improve health and well-being.
  6. Sustainable use of resources: BNG principles promote the idea of ‘building with nature’, encouraging the use of sustainable resources and practices in development projects.


Overall, BNG is a practical approach to meeting the ambitious goals of the 25 Year Environment Plan, helping to ensure that our environment is left in a better state for future generations.


“We have retained Indigo Surveys to undertake measured surveys and tree services for various projects over the last 5 years and have always found the price, quality and customer service to be excellent. Andrew Turnbull is exceptionally helpful, easy to contact and always responds to queries in a timely manner.”

Claire Williams
Project Manager

“I have worked with Indigo on many school projects. Many ran at the same time and had very short pre-construction programmes. Indigo were proactive and able to meet the challenging programmes, which enabled us to meet all submission dates for approval. We were kept aware of all ecology/arboricultural issues from the outset.”

Jane Shaw
Senior Design Manager

“Indigo’s role in the Project Team was crucial in obtaining Planning Permission on a complex and challenging site. Their expert arboricultural knowledge resulted in successful negotiations with the Planning Authority and helped make the project feasible while also ensuring that it preserved the character of the site.”

Graeme Mill
Project Architect

“We used Andy at Indigo Surveys for a difficult planning scheme in Wimbledon Village and found his knowledge and strategy in dealing with the various issues thrown up very impressive and the added footprint that this gave the client on the scheme was invaluable. We continue to use Indigo Surveys Ltd for Arboricultural Consultancy services, and would be very happy to recommend them.”

Martin Down
Managing Director