I’ve seen people worry a lot about what to ‘do‘in their gap year, but honestly, working as much as possible and saving some money will make your first year so much easier! You can visit friends at uni, and just take a break. I think it would be a great idea if everyone did this- I think it would improve university experience for many. Good luck whatever you choose.
(And LSE and UCL will want to see high predicted grades to give offers)