That stat on Bromley is such a good one and a great pub quiz question!
As regards the board, South Wales Central gave 40% of it's vote to Labour in the last senedd elections but only 46% turned out to vote, so only around one in five voted for the main left-of-centre party and many of them would have been centrists or even socially conservative Labour supporters so to conclude I think the board is still disproportionately populated by raging leftard loony trokskyite commies etc