Imagine a group of people round a table, talking after a meal. They are an ecologist, a landscape architect, a garden designer, and an architect. As is natural, sooner or later the conversation turns towards development. The ecologist says:
‘All development is bad – it causes huge damage.’
‘Who are most of your clients?’ asks the architect.
‘Developers’ comes the answer. The discussion goes on and eventually the ecologist suggests that ‘If we could have a law that made sure that all development added to biodiversity, then I would sleep easier.’
We do now have such a law – a world first, of which we should be justly proud. Perhaps it could have had a snappier title than: ‘Schedule 7A of the Town and Country Planning Act 1990 (as inserted by Schedule 14 of the Environment Act 2021)’. However, everyone refers to it as Biodiversity Net Gain (or BNG). It is a huge leap forward.
So how was it that I found myself on a stage a few months ago with two eminent ecologists (one of whom helped shape the legislation) and a lawyer, arguing that the legislation did not increase biodiversity in many cases. I began to ask myself what I was doing there when one of them said – ‘I could not disagree with John more.’ I had been very dubious about taking part in the debate but was assured by the organisers that I was on the panel precisely because I wasn’t an expert, but a practitioner. So let’s dig a bit more into this.
BNG works best for potentially damaging urban fringe and rural development. Here land is cheaper than a city centre and there is potentially more biodiversity to damage. So a ‘tax’ that favours increasing biodiversity on site, or as a next option nearby, is obviously a good thing. BNG tends to prioritise habitats and particularly native flora over anything else. This is understandable given the loss of habitat in the UK since the second world war.
Urbanisation in the UK is now at around 85%1 (i.e. percentage of population living in urban areas), suggesting that most planning applications are in urban areas. And this is the crux – most of these sites do not have pre-existing native habitats. In such developments, space is limited, so the non-built areas must work hard – for circulation, screening, shading, softening of built structures, play, seasonal appeal as well as biodiversity. It is difficult to achieve all this with the constraints imposed by BNG.
We recently worked on a car-free development in London. It was on a heavily degraded but previously undeveloped site. Two ecological surveys gave it very low biodiversity rating. Our proposals were based around biophilic principles – the human need and desire to be in natural spaces. Even with the density of the development, we managed to achieve all of the above, including a diverse environment and some ‘non-access’ areas. Despite this – and the endorsement of the team’s ecologists – the scheme registered a loss of biodiversity under the BNG metric, instead of the plus 10% that we needed. The ecologists did not think this could be right, so we had the figures checked by another set of experts, who registered a similar score. So, even though we achieved more biodiversity (and human benefit), we scored lower on the BNG metric.
My point here is that biodiversity and native habitats are not the same thing. The work of the Sheffield University Landscape School is a good example. These are extremely biodiverse environments, human friendly, low resource input, suited to city centres, but which would score low on BNG.
What most garden designers want to know is will the regulations affect them, and if so, how? The short answer is not much. Householder applications are exempt from the legislation, as is custom build. Small residential developments (nine houses or fewer, on less than 1 hectare of land) are affected, but the requirements are less onerous. There are some useful tools on the gov.uk BNG pages2. For small developments, the calculations can be done by a garden designer or landscape architect rather than an ecologist, using the Small Sites Metric tool. In any case, we should all be designing with biodiversity in mind, regulations or no.
Back to my argument on stage: ‘Birds and insects do not read the books’ I said, perhaps somewhat rashly, but to make a point. Nature is opportunistic – the birds in my garden will gorge on the berries on the Amelanchier (a native of North America) and the goldfinches adore the Lemon Balm seeds (a Southern Europe native). We must recognise and harness that opportunism if we are to achieve biodiverse environments in the dense surroundings of our cities, and if they appeal to people as well, then nature has a better chance. This argument did not go down well with the ecologists on stage, but I stand by it.
So, although Biodiversity Net Gain regulations are a huge step forward, I think they have some way to go to work well in urban environments, which is where the bulk of development takes place. I was talking about this to an ecologist friend (who works for Natural England) recently. He agreed but made the point that they were now having different conversations with developers – indeed they were having discussions that just would not have happened before the legislation. And that can only be a good thing.
Footnotes:
Banner image credit Unsplash/Kristine Cinate
May 13, 2025
