Hertfordshire County Council has drawn up plans to help protect the county's biodiversity amid new housing projects – with Biodiversity Net Gain (BNG) plots of land to help offset loss of wildlife and carbon emissions.

Already, the council-owned Westmill Farm, northwest of Hitchin, has been identified as a suitable site for BNG – which could harbour up to 200 'habitat units' to compensate for new developments.

It is proposed that the earliest BNG units will be created at Westmill in early 2025. The BNG units can be sold to services or put on the open market, where developers can purchase them as part of their BNG obligations.

A report titled 'Biodiversity net gain on the Hertfordshire County Council rural estate' was discussed by members at the council's resources and performance cabinet panel.

The report revealed that Biodiversity Net Gain (BNG) is an approach to development that "aims to leave biodiversity in a proven better state" than before construction took place.

As a practice, BNG was introduced by the Environment Act 2021 and went into effect on February 12 last year. It obliges planning authorities to ensure that new developments provide a minimum 10 per cent net gain in biodiversity.

The document stated: "To measure this 10 per cent uplift, a universal metric has been created that seeks to quantify the biodiversity by classifying different habitats and the general condition they are in. For example, a woodland in good condition would support a broader range of species and therefore greater biodiversity than a woodland in poor condition.

"To provide a worked example a 10 acre grass field going to residential development may currently have a biodiversity baseline of 20 units, the developers must therefore deliver a residential housing scheme which also provides 22 biodiversity units.

"It is expected that a lot of developments will deliver this 10% uplift on site, by planting new hedgerows and trees and meadow creation."

However, the report adds that in some circumstances, site constraints may require off-site delivery of BNG units. Possible off-site deliveries could include grassland creation, woodland and hedgerow planting, scrub or even wetland creation.

Westmill Farm is being earmarked as an ideal hub of BNG units, suitable for off-site delivery for new projects such as schools. The council acquired Westmill Farm in 1914 and it can still function as a farm even with BNG status.

The report states: "Westmill Farm, to the north west of Hitchin, was considered to be a suitable site as the tenancy was due to be re-let, it's boundary on one side is a chalk stream and a nature reserve, it's on the edge of the Chilterns Area of Outstanding Natural Beauty, has potential to form part of the Local Nature Recovery Strategy (LNRS)."

"A new tenant has been selected who will farm both the BNG area and the rest of Westmill Farm. They have an existing sheep flock which they plan to establish on the farm, as well as small scale livery and shepherds hut. Even without the BNG element, this letting meets many objectives within the corporate plan, such as promoting a cleaner and greener environment and providing a revenue return to support the wider service."

Cllr Paul de Kort said: "I think this is an extremely good idea."

Cllr Ian Albert added: "I support this. I think this is a really interesting development and it's definitely the right way forward. I think it will be much welcomed in an area where people are concerned about further developments. Having this there is a really important thing."