I've been twice, in 2018 and early 2020 (just before lockdowns started).
For London
- I don't know what the locals would have to say about driving in London but as a visitor it looked like a nightmare. We used transit to get everywhere, it was surprisingly cheap and easy. Just avoid the trains during rush hour (we would just find a pub to wait it out), and check for line closures before you go out for the day.
- as mentioned the RAF London museum is 100% worth it. Free entry but you can sit in a Spit XVI for a fee. Great WW2 and WW1 exhibits. My wife even enjoyed it. Though I still had to go to a musical that night as payment haha
- most public museums are free. We picked up a pass our first trip that covered all the tourist places. Churchill war rooms, tower of London, tower bridge, Westminster, st Paul's, and HMS Belfast were all included I think. Ended up being a lot cheaper than buying tickets individually.
- explore the pubs, if that's your thing. Some great old pubs hidden away, dating back centuries. My faves : prospect of Whitby (pirate pub on the Thames), ten bells (jack the Ripper victims drank there), ye Olde Mitre, Cheshire cheese, and if wine is your drink Gordon's Wine Bar by Charing Cross. Really can't go wrong
-hampton court was really interesting if you're into Tudor England. It's a good day trip. IIRC there is an entrance fee
Outside of London:
- we mostly travelled by train, but that was really easy to do. We have friends in Aberdeen that drove us around a bit. Get used to backwards traffic circles, they go through them kinda aggressively.
- Aberdeen itself is more of an industrial city, mostly supports the offshore oil rigs. Has a really nice beachfront though. And great hiking just out of town
- Leeds is a really cool town during the day with friendly ppl. It becomes a whole different beast at night, at least where we were staying. We stopped in Leeds because my wife's ancestors were from there. Found their marriage records at a local church. Also the royal armory museum was well worth a look.
-if you're going to Scotland (some of my ancestors were from Scotland), highly recommend checking out Isle of Skye. Did a 3 day tour there and it was amazing. Really relaxing and beautiful scenery.
- Edinburgh is a cool city, though only stayed one night. Edinburgh castle is something to see.
- Glasgow is ok. It's a great jumping off point to explore the rest of Scotland