At the moment, travel is illegal unless for work or emergencies. It’s even illegal within the country at the moment, never mind abroad. I think NellG is right, people will simply not comply with the restrictions if they are continued. I think it’s already happening, or at least, a wide interpretation of the word bubble is already in use. I’ve seen this in action myself.
My 93 year old mother was totally isolated for twelve weeks in the first lockdown, we got her shopping and delivered it to her door and that was it. I refuse to do that to her again, it’s cruel. As we’re in a bubble with her it doesn’t matter, and she has carers going in now that she didn’t before. She still got Covid so all our efforts didn’t make a jot of difference. She fell and went into hospital, and picked up Covid there, and of course, we then got it too (support bubble.)
How long can these restrictions last? I definitely think people will stop complying if it goes on much longer.