theoretical physics at ucl or imperial?

Applied for both as well.
Please do not disregard UCL just on the basis of prestige. Even so it is quite comparable to Imperial.
I know a lot of people criticise UCL for some reason but UCL physics is actually good. I had an offer and was invited for an offer holder day and have come back quite impressed. They have the biggest department of physics in the UK and have over 500 member faculty. I really liked their research and labs. They also have quite a friendly atmosphere.
As for Imperial, I visited their physics department on open days. While I liked everything about it, I was not that taken by it. Maybe it's just me. Don't get me wrong, their research is good, the faculty is nice but it's too academic and I am looking for a more rounded approach than pure academics. Still I do prefer a rigorous course and would like to have a good degree. For me UCL ticks all the boxes.

You might be different to me so just select based on that. I am yet to receive an offer from Imperial but even if I do I will firm UCL. I am just waiting for the kicks and if UCL accommodation opens first then I will just withdraw my application from Imperial.

I got my offer mid January. There were 25 other offer holders as well so they have been giving offers just not a lot. I had my offer day in February term break.

I have 3A stars predicted. Offer holder day was a personal invite. It is what the physics department does, they don't invite more than 30 in one go. They don't have any pre-set days. You will see when you get an invite. You have lunch with someone from the physics department and fellow offer holders. Current students talk to you, talk about their experience and answer any queries. You get a tour of the department and the labs, you get to meet a few PhD students and talk about current research. There is a welcome talk from professor Raman (head of department) and a guest lecture with a q&a session.
You can talk about modules, course structure, anything that's on your mind. It is quite an insightful day. It is a 3 hour event.
Campus tour is not included but you can book a separate one on the same day or take a self guided tour by yourself.

You can go to most common areas and cafes on a self guided tour. It covers the same areas as guided campus tours, the only difference is with guided tours they tell you which building is used for what purpose and extra info on UCL life. I did both but enjoyed the guided tour more. You can't visit individual departments as you need a key card but you can't visit even with a booked tour.
Guided tours are available almost every day. I have seen some people joining them even without booking as no one is checking your booking confirmation.They run every hour.