The proposal from the energy regulator Ofgem is to require a sufficiently-sized deposit to demonstrate serious intent to build.
It's not an additional fee: if you go ahead and build, it's cost-neutral. It's only an additional fee for speculative proposals, most of which wouldn't go ahead.
https://www.ofgem.gov.uk/press-release/ofgem-acts-free-grid-...
https://www.neso.energy/news/unveiling-new-project-pipeline-...