Interesting. I think both of your numbers for UK politics are too high. Going only by what you say here, I think your number for sex with men are also too high - fewer than 10% of the men I know who identified as straight at the start of the decade had sex with a man during it.

This seems to be an overconfident assumption of knowledge about private lives. (Especially if 'you know' is a sufficiently relaxed category for the sample size to be anything but trivial.)