There's enough options (competitions, discount ticket groups, Groupon-esque things, corporate giveaways etc) to discreetly fill any unsold venues nowdays, and with the cost of living thing making people be a bit more picky about what they're buying, organisations like Live Nation will have this sort of thing built into their projections for the tour. My boyfriend works in theatre and it's very common to be doing discounts now, and we'll be seeing much more of this with live music. Ultimately they just want people through the door buying booze/merch/etc.
I'd be surprised if they couldn't sell out London/Manchester/Brighton through homosexuals alone, but some of the smaller regions and closer cities like Edinburgh/Glasgow might split the vote a bit. Honestly though, who knows?