>The Greens are a niche party in the UK

Are they really?

https://en.wikipedia.org/wiki/Opinion_polling_for_the_next_U...

Pretty much, especially with their latest mess with “Zionism is racism” entryism, a leader who can’t lead, and a split between those interested in green subjects and rump Corbynites

They don't seem to be terribly interested in the environment for a 'green' party.

UK is a First Past the Post system. It doesn't matter what their national polling is, if it's going to result with exactly 0 seats in the parliament.

Whatever info you’re working from is out of date. The Greens currently have 5 MPs: https://members.parliament.uk/parties/commons