Will I need AC in London in August?

No way to know. I've been in London in August when the weather was perfect and also when it was so stiflingly hot that Londoners were sleeping in their marginally cooler basements for relief. I was glad to have AC then. I would go with AC if it's more than a night or two, which you could bear before moving on.

I think you will prbably want the AC. Some summers have been coolish when we were there, but others were very hot and humid- remember you are on the river and not that far from the ocean. Those of us from my part of the country know that combination can make for some VERY uncomfortable nights if you don't have AC. Pack clothes that breathe, too. AND pack things you can layer if it is a bit cool. One thing about British weather- you just neverknow what you will be dealing with.

The average temperature for August is 70. It does get higher at times but I really think you will be fine without AC.

Sometimes I've been fine in London without air conditioning (weather has been moderate) but, as others have said, sometimes it can be miserably hot. I would certainly look for AC to be on the safe side.

Based on some of my experiences i would always opt for air conditioning. At some hotels we have been able to get fans which were better than nothing, but airconditioning would have been much more comfortable.

Really comes down to what you're used to. Europeans tend to not understand North Americans obsession with air conditioning and this is reflected in most hotels not seeing it as a priority to provide it. Much of what air conditioning is provided is kind of half hearted. If you get an unusually hot spell in August (about 85-95F during the day) then I would have thought you may wish you had it, but not at the normal tempertures of abou 70-75 F.
August is one of the wettest months of the year, mostly light showers so it can be humid. Things like visitor attractions and retail outlets similarly don't see it as a priority to provide air conditioning during the day and none of London's public transport is air conditioned.

"Things like visitor attractions and retail outlets similarly don't see it as a priority to provide air conditioning during the day and none of London's public transport is air conditioned." Which is why I for one would want AC in my hotel so I could cool off. And if you are used to sleeping without much noise from the street, you may need it so you don't have to keep your windows open.

I'd go with having AC. The last 2 times I was in London in the summer it was over 90 degrees. Global warming has been quite noticeable in Europe the last few years.

After we have had a few days of summer in July, we always look forward to August, hoping against hope. And, 9 times out of 10, August lets us down. Its always colder and wetter than we would like. September often has a few better days. News Flash - the sun came out yesterday!!!

Richard, if you have the choice, go for the AC. You can always turn it off. August weather should be pretty comfortable. But, remember that an average temperature of 70F doesn't mean the temperature is usually 70F. London is a large and crowded city, with lots of brick, concrete and pavement to keep the heat in. The Tube can be stunningly stifling in summer. And you'll be out and about being active. Trust me, you will be pleased when you duck into a shop or a pub that's running the AC.

I think you should choose a hotel with AC. The first trip I made to London was with a tour group many years ago (not Rick Steves; I made a mistake letting a travel agent book us with a run-of-the-mill tour operator) , and they booked us into a hotel with no AC. No problem, they told us at the hotel; you can open the windows for air. We got to the room, opened the windows, and a crowd of pigeons began to gather on the windowsill. No screens on the windows! I guess the birds had been fed by previous visitors. They peeped curiously in the window as though they were all going to come in, and pooped on the windowsill! Also, there was a fire escape right outside the window, so that would have provided access to intruders. We asked to be moved, but were told none of the windows had screens, so we stayed where we were and kept the windows shut, in August, and yes, it was hot. So I would say find a hotel with AC, you'll be glad you did.