Gay and pro-gay voters would never Vote UKIP with a gun to their head. They are caving in for NOTHING.
You are judging Britain by the US’s social standards. Christianity is still relatively influential in the states, but over here, only a small minority really take it seriously, and even people on the right and the undecideds are at best, largely indifferent to the issue of gay marriage, if not actively in favour of it (Tory support for it wasn’t just Cameron acting in a vacuum).
All the non-fringe parties are in favour of gay marriage, it is a dead issue here, and it will just have to be chalked up to an issue that is part of the liberty of individual conscience and move on to issues which are not lost causes. If people turn away from UKIP because they now offer a begrudging acceptance of gay marriage, who else are they going to vote for?