London, late May or early August???

Late May/early June in London, weather permitting, is a lovely time to visit (on average August has more rainfall, but who knows!). The early summer flowers in gardens, squares and parks are in bloom and everything looks fresher. As will the countryside. The daylight hours are at their longest, it does not get really dark until after 10pm so good for daytrips.

Everything will be up and running.

In May there is the soccer world cup and possible UK elections, traditional times when people don't travel. London tends to be a ghost town when there is a match on.
August is one of the cheaper months in London as UK kids only get August off for summer holidays and all the businessmen that normally fill the hotels are away.

Both ways you should get some good last minute discounts

World Cup starts in early June..... Mexico vs. host SA on June 11.

England opens against USA on June 12 -- it'd be fun to be in London for that one, especially if we pull the upset!!

Buckingham Palace won't be open to the public in June, but it will in August. I would suggest making a list of everything you really want to see and then making sure nothing's going to be closed at certain times of the year.

All the school kids in the UK are off in August so you might run into a lot of UK families on holiday. I have been there in both May and August and have not found anything closed in May. Buckingham Palace is only open for two months per year which in August and September. They started opening it for two months to help pay for the repairs at Windsor Castle after the big fire in 1992.

Go in May, avoid the crush of American tourists off for Summer vacation.

I was there in May and thought it was ideal. I did get caught in one downpour, otherwise the weather was perfect and the crowds were very managable.