Firstly anyone who has sex with men AND women ISN’T, strictly speaking, gay. But there’s no way he should have said what he said when he says he wasn’t gay. It’s just obvious he was setting himself up for this.
And secondly, the Tatchell thing. You can see the by-election literature youself here — and it does include the phrase ‘A straight choice’. BUT — was straight, meaning not gay, common parlance in 1983? I don’t know, I was 5! (And at 5, I thought it was great to be gay — after all, the Famous Five were. And the Famous Five taught me to read, because my parents couldn’t read it aloud with a, erm, straight face). AND we also used the phrase two years later in Brecon — it’s part of the technique we call ‘third party squeeze’. These days, it manifests itself as barcharts and ‘two horse race’ metaphors.