@simon_brooke I used to live in Lewisham (I moved away 10 years ago). There has always been a significant minority vote there for the Greens and they have easily been the second choice of voters with about 30% of the vote to labour 60% but frustrated by the FPTP system,. In my time they even had one or two councilors.
These days there are many reasons - including the Labour Party sell out to Israeli interests on Gaza - why some of the previous Labour voters are now defecting, it's not that the voters have changed it's their perception of what the two parties respectively stand for that has.