Just because homosexuality is casually acceptable in the UK, doesn't mean that the general public actually likes it. It just means that they know they have to (begrudgingly) put up with it.
As you know, the British tend to be a largely tolerant lot who mind their own business, but if they see something they don't like they can and do push back against it. Think about this: there have always been gay couples in the UK, and certainly throughout your entire lifetime. How many have you seen on the High Street holding hands in public? Hugging each other goodbye at the train station? Kissing (even a quick peck on the cheek)?
Exactly.
We've learned the hard way that other people might accept the fact that homosexuality exists, but they don't want to witness any evidence of it; they get very NIMBYish about it. The Daily Mail mantra that always makes me laugh is that they don't want it 'shoved down their throats' (how very Freudian!).
Fortunately, things are changing. I'm delighted to say I've seen quite a few lesbian couples holding hands in public over the past few years - and let's face it, the change has to start there because we don't have the same societal aversion towards two women holding hands, which makes cis lesbians less likely to be the victims of the sort of casual aggression that occurs in these specific situations (just look at Elis's description above of being read as a lesbian couple). People do occasionally harass lesbians, but they're much more likely to harass gay men.
I've also seen a grand total of two(!) gay male couples holding hands, in two different cities. But you should've seen the looks on their faces: wary, guarded, on edge; just waiting for some idiot to have a go at them. But the more gay couples do this, the more accustomed the public will become to it. It's getting better, but it's going to take a long, long time before two men holding hands in public is NBD.
Until then, be aware of your surroundings... and be careful.
