The London Borough of Sutton: improving biodiversity within planning applications

The London Borough of Sutton share their approach and experience of securing no net biodiversity loss for two recent planning proposals. Please note - Councils developing BNG approaches in advance of its mandatory introduction may have to adapt their approaches to comply with the details of legal requirements in November 2023.


The London Borough of Sutton share their approach and experience of securing no net biodiversity loss for two recent planning proposals. Please note - Councils developing BNG approaches in advance of its mandatory introduction may have to adapt their approaches to comply with the details of legal requirements in November 2023.

Photo of a digger in a pond
River restoration on the Wandle chalk stream as part of the Corbet Close redevelopment


The London Borough of Sutton (LBS) first introduced biodiversity requirements for developments in their Local Plan, adopted in February 2018. The biodiversity policy states:

Major new development should result in no net loss in biodiversity value, as assessed against the DEFRA biodiversity offsetting metric, the Environment Bank Biodiversity Impact Calculator or any metric which the council subsequently adopts formally.

A key dimension of this policy is the explicit reference to a metric to undertake biodiversity evaluations. This was before the release of version 2.0 of the Defra Biodiversity Metric.

Sutton’s Technical Guidance Note, published in April 2018, supports the Local Plan and outlines the specific biodiversity requirements developers are required to meet, including use of a bespoke calculator. This metric is preferred by the council since it quantifies an action to any net loss which can then be articulated in offset monies and has a detailed range of green roof habitats - important given their value in the urban context.

The council subsequently adopted a Biodiversity Strategy in 2019 which recognises the introduction of mandatory Biodiversity Net Gain (BNG) requirements through the Environment Act, as well as setting costs for their ‘Biodiversity Tariff’, used for determining compensation values to reach No Net Loss. The Biodiversity Strategy is also critical in providing opportunities to undertake offsetting through setting out actions to create new habitats or improving existing habitats. Ultimately, this justifies the use of Section 106 agreements since LBS has identified specific site opportunities for offsetting and habitat banking.

LBS is now considering how best to prepare for the introduction of mandatory 10% BNG in November 2023 and hoping to go above 10% in its local policy. This will perhaps be delivered via a zonation-based approach that accounts for the ease of delivering BNG in different circumstances. It is anticipated that this will be easily achievable in the urban centres, as so little vegetation is impacted, whereas even 10% gain may be very difficult when considering back garden loss.

Small-site example

timeline of a small-sites planning application

A planning application was submitted to LBS in August 2021 for the proposed demolition of an existing bungalow and erection of a two-storey detached dwelling with a detached double garage. The site is part of Sutton's extensive garden suburbs, part of a gated community, on the fringes of the green belt with Surrey. 

LBS’s validation information states that planning applications for an area over 100 m² must include a Biodiversity Net Gain Assessment. The original planning application did not include this report, so it was requested by the planning officer. The applicant submitted the report in February 2022, outlining a net loss of -17.65% as compared to the site’s existing biodiversity value of 0.06 units.

LBS offered two options to the applicant:

  • Pay a biodiversity tariff of £5,614.20 to offset the 0.06 units


  • Produce a Biodiversity Enhancement and Management Plan which incorporates on-site BNG measures to offset the loss.

The Biodiversity Team felt that the planning conditions required to deliver BNG on-site would have been, in this instance, too onerous and not proportionate with the scale of the development for the landowner to undertake for the next 30 years and, therefore, were willing to accept the compensation value (tariff) to go towards habitat banking within Sutton.

The applicant decided to pay the tariff, which was secured through a S106 agreement. Despite an agreement being reached on biodiversity, the application was subsequently refused on other grounds.


Large-site example

Image showing a timeline of LBS's large site BNG example

A planning application was submitted to LBS in November 2018 for the redevelopment of redundant wastewater treatment works to construct four industrial units. The proposal also included the restoration of a former sludge bed close to the development site to create a new ecology area.

The developer had previously sought pre-application advice from LBS in July 2018 which included a site visit with the council’s ecologist. The ecologist advised the developer that the Warwickshire Model that they used to quantify the biodiversity of the site was different to the Sutton Calculator, adopted through Sutton’s Technical Guidance Note. The developer submitted the planning application in November 2018 with an Environmental Statement declaring that:

The significant package of measures at the… site will ensure that losses are fully mitigated, and that an increase in species rich and diverse habitats is delivered, which will achieve a net gain in biodiversity terms.

The developer provided an outline ecological delivery, management and monitoring strategy in February 2019 which provided details on how they intended to offset the biodiversity loss through the creation of an ecological reserve. Further discussions took place between LBS’s ecologist and the developer to reach agreement on the scores for habitat loss and creation on-site. In April 2019, agreement was finally reached between LBS and the applicant as to the values for both the old sludge beds and the offset site. This led to a Net Loss of -3.31 units, across both sites.

Due to the size of the net loss, the applicant had to create not just the offset of c.3ha but also pay compensation. The costs of the offset were deemed to be c.£1 million pounds over 30 years. A further c.£250,000 compensation was also agreed to undertake biodiversity offsetting on a river restoration project on the River Wandle and to fund the employment of a second biodiversity officer.

The development was approved by planning committee in April 2019.

Key challenges

Awareness and communication of BNG requirements:

LBS have found that the main challenge when implementing a biodiversity policy is that applicants are often unaware of requirements when they apply for planning permission. A significant amount of information needs to accompany applications upfront and if not provided, this leads to delays in the planning process. LBS’s Biodiversity Team are working on identifying ways to communicate this with prospective applicants.

This includes writing articles on both council and third-party websites which clearly communicate what the council requires on BNG and simplifying online information via the council website and related channels which will also ensure that time-strapped consultants, designers and developers can understand what is required. Finally, LBS are working with the local environmental record centre to help identify key documents and BNG information that can be shared via consultant data searches ahead of a project to stream-line the process and reduce errors. 

Monitoring and enforcement

LBS have found that monitoring of habitat delivery once planning permission has been granted is one of their most significant challenges.  This is particularly the case for the ongoing biodiversity scheme within the large-scale development outlined here. The biodiversity team is concerned that several years after the planning application was granted, the offset site is still not in a satisfactory ecological condition.

Adequate experience in designing habitats has caused substantial delay securing high quality habitat through the design and implementation stages. A lack of understanding and limited scope for collaboration has also caused frustration and missed opportunities.

While the biodiversity team acknowledge that there have been issues which are no fault of the developer, such as the presence of barn owls on the site affecting the timing of some works, they also recognise that the developers have not delivered on their environmental duties set out in the management plan.

While this is an ongoing challenge for the council, the biodiversity team has ensured that it has a productive and respectful working relationship with the developers, which has allowed conversations to address the offset site issues to continue constructively over the years.

Advice to other authorities

Scrutiny of applications

London Borough of Sutton recommend that other authorities looking to implement new biodiversity requirements recognise that applications often require extensive expert scrutiny. This is because applications are often written by consultant ecologists, many of whom do not have a background in habitat management. They recommend that, wherever possible, councils should have access to an ecologist who has a background in habitat management and biodiversity, to be able to effectively assess planning applications, as this will be key in understanding if what is being submitted is realistic, achievable and suitable in their local authority.

Consistency of approach across policy documents

LBS recommend that local authorities should include specific environmental targets across all adopted local biodiversity policies and action plans.

For example, their Biodiversity Strategy identifies that:

At least 60% by number of plant individuals and species variety to be planted will be native and local to the area

This is then used as part of the condition wording, to ensure developers move away from more generic landscaping schemes and consider how they can deliver multi-functional benefits through landscaping. Conditions around landscaping, green infrastructure, habitat creation, features for wildlife etc. are all very specific, so the Council has control over how developments achieve its vision.

LBS is therefore in a strong position to be able to negotiate and reach agreements with developers because of the continuity and cohesion through both planning policies (Local Plan and TGN) and the Council's vision for nature in the borough (Biodiversity Strategy), which provide different but consistent strands of support to achieving its aims through planning. 

As such, it is difficult for applicants to argue against the inclusion of a net gain for biodiversity within their development plan, because there is so much adopted policy support.