Not-too crowded places, Sun/Mon post-coronation?

well my crystal ball is very hazy, but a wild guess would say that if many many tourists went to a city for a major event and stayed there, there might be big crowds on the holiday. maybe not, but who knows.

I will say that on a normal Monday and Tuesday, Borough Market is as dead as a dead thing. That's because the huge proportion of stalls and brick and mortar are closed.

From your list, my personal opinion is that the busiest of your list would be the Tower of London and the Churchill War Rooms. If you want to go to either of them, I'd get timed entries for opening time for each venue.

I think the British Museum will be crowded but perhaps the British Library will be less so.

The British Museum has always been very crowded (by museum standards) on my recent visits. Waiting time in line was around 30 minutes shortly after morning opening time in September. The first floor--especially the Egyptian exhibition--seems to be the most crowded. The situation tends to be worse on weekends/holidays (local families, I assume) and on rainy days, or so I have been told.

The Tate Modern and the National Gallery are popular but have not been as mobbed for me as the British Museum. In the National Gallery you can expect to run into localized clumps of people around the most famous/popular paintings, like Van Gogh's Sunflowers, but I've never been uncomfortable there because of crowds. That said, I haven't been to the National Gallery since 2019. The Tate Modern feels airier and was less crowded than the National Gallery on my visits between 2017 and 2019.

Purchasing a (timed) ticket for the Churchill War Rooms in advance is a must; the ticket line tends to be very long, and the ticket you will be able to buy when you get to the head of the line will probably be for an hour or more in the future, not for immediate entry. You might also encounter a total sellout. Be aware that if you're interested in the Churchill Museum part of the CWR, you can easily spend over half a day seeing the entire CWR; in that case, don't opt for a late entry time. I went to the CWR in 2019 and don't know what it's like now; the war rooms themselves were tight quarters and very crowded. The Churchill Museum was also quite busy but had a bit more space. If you only want to see the war rooms, not the Churchill Museum, take a look at the high entry fee and consider whether it will be worth it to you. The Imperial War Museum is excellent and very large. It, too, is popular, but it hasn't been as crowded as the CWR on my visits.

You might consider the Courtauld Gallery. It reopened not too long ago after an extended renovation. It's not on as many people's radar as the National Gallery.

Check websites for all the attractions you're interested in to see what they say about being open, or not, on bank holidays.

If you end up casting around for something interesting to do, consider taking one or more London Walks. They have a broad slate of walking tours priced at 15 GBP each. I see more than a dozen tours listed for May 7 and ten for May 8. They encourage prebooking (you don't currently pay in advance), but I was able to simply show up at the meeting point and take two or three walks in September. I guess prebooking might not be a bad idea for your time period, because if 25 or 30 people showed up, I suppose they might decide to restrict the tour to those who had prebooked. (I'm just speculating.) I should note that there may be adjustments to the list of tours offered while you're in London; just check the website from time to time.

I’d say bigger issue than the bank holiday is the coronation on 6 May, the day before your arrival. There will still be loads of people in London for that, and the road closures related to the event may well still be in place through the weekend. They were on the day after the Queen’s funeral; as pedestrians in the Hyde Park—Green Park—St. James Park area we had to make some wide detours around barriers. You may not even be able to approach the entry to the Churchill War Rooms.

Yes, I'd look more at the Southward, Borough Market area. Also as someone pointed, definitely do a London Walk. They are my favorite walks(used to go to London every year) and happen rain or shine. I'm sure they will offer something on that weekend. I saw lovely Hampstead/Highgate with them and even visited Kensal Green Cemetery where you can see the crypts of rotting wood coffins.

Your list of options are, as you noted, all very popular. I personally wouldn’t go anywhere near any of those on coronation+bank holiday weekend. Consider Dulwich…had a very pleasant half day there prepandemic…Dulwich Picture Gallery (oldest public art gallery in England, closed Mondays), shops and restaurants, families enjoying the park, etc.

I inadvertently booked a trip to London during the Platinum Jubilee in June. I joined the crowd lining the Mall for Trouping the Color but after that had difficulty making my way across central London to meet a London Walks…diversions, tube station closures, etc. …just allow plenty of time.

Windsor? Canterbury?

Any of those are going to be very busy on a bank holiday weekend. There will be normal tourist traffic + UK families visiting the Capital on the school holiday. The City of London should be quiet due to office closures, so a walking tour there could be a bit of a reprieve. But, realistically, if you are locked into those days, be prepared to deal with crowds.

Thank you all for valuable input. I'm rethinking dates, not totally locked in. It would mean reversing itinerary. Then I would end up in London second to third week of May. I'm trying to look up, when school holidays start. I'm wondering if it would be another very crowded time.

Please pardon I know there was at least one other thread about this - King's coronation and school holidays, with deliberations between the two.

summer half term tends to be around the Late May Bank Holiday, but can vary around the country, and between state schools and fee paying schools.