It will happen. I'm planning on Romania in August for a 5 day break
May 17th to maybe mid June it will be restricted as hell with quarantine and whatever the destination country throws at you. Nobody will bother aside from people willing to fork out the money.
June-July it will be less restrictive but flights will probably be expensive alongside the fact that we'll be opened up here so people will be more open to the idea of staying put. Maybe this will be the point where family members abroad can visit without £200 worth of tests and quarantine.
August, as we were last summer barring a variant issue, but again, a lot of people priced out of it because of the demand. Honestly, best bet for people is early September to somewhere that's still warm like Almeria
When someone like Mike Tildesley says that for the average person, travel is unlikely well....a solo traveller visiting family or going for a city break isn't the average traveller, not over the summer anyway.
I'd add just look at the article in the Independent today about how they haven't actually dished out any fines thus far, strikingly similar to the whole quarantine process from last year, and how it was a big show...
I can't lie, I'm biased in this as someone who loves to travel, but I think looking at all the signs, plus comparing where we are now vs last year (and I got away 3 times last summer...), I think it'll be a case that while they'll be restrictions, it's most certainly going to be possible