Same reason I have issues with the Uk Green party, makes them look foolish when they push to stop fossils but the only current practical solution is nuclear(which they're against)
Solar, wind, and tide are very dispersed forms of energy, so harvesting them on a significant scale has a massive environmental impact. Also there are issues relating to extracting the input materials, and to waste disposal after the devices are retired. It's not clear to me that "green" energies are any better than fossil fuels.
But we will need baseload power for a long time to come. The UK is not investing in battery technology and on still winter days the UK needs to be able to spin up a lot of power generation quickly. That role is currently filled by natural gas. Nuclear should have taken its place.
Nuclear can't do peak load scaling and is less consistent than you might think for baseload.
You might benefit from looking at systems like Compressed Air Energy Storage. Highly responsive, compatible with CHP, virtually no scarce materials involved, and pairs dramatically well with renewables.
As an additional bonus, it also doesn't leave vast tracts of land uninhabitable if it goes wrong.
