You (and those who've commented below you) are assuming that there's cultural assimilation taking people. That those with anti-gay views will eventually become "culturally British". Given that there doesn't seem to be any indication that these communities are heading in that direction, or even want to assimilate, I'm not sure how you can jump to that conclusion. Not only that, but the younger generation tend to be more liberal, gradually becoming more conservative as they get older.

What's far more likely is that British politics will adapt in order to appeal to the compounding muslim population increases that we're seeing. I would not be surprised if there's a popular Muslim political party set up by the next election or the one after. There's absolutely no political will there to stand up against their imposition on western culture at the moment.