euros

Why would you want euros in London? If you are going to go to the continent to a country that uses the euro, you can easily wait until you get there to get them for an abundance of ATMs. That is usually the best exchange rate.

Probably not as ATMs give local currency because it the locals who use them the most and not tourists. However, you might check the EuroStar station or the airport. And, of course, the money exchanges will get you by till you hit a Euro country.

I have no experience with London ATMs, but in Zurich, Switzerland their major ATMs offered both CHF (swiss franc) and euros. You may find some like this in London (but honestly I have no clue and don't want to recommend it) or you may just have to wait until you arrive in a euro-using country. If you feel you definitely need euros in London, there are exchange booths in London.

Not usually. Just possibly at airports but I'd expect a dreadful exchange rate.

I have seen euro dispensing ATMs at Heathrow and at St. Pancras station. As others have pointed out, it will be an expensive way to buy euros. You will get hit twice, you will pay to convert your dollars into pounds and then pay to convert your pounds into euros. At a guess you would lose more than 15% on the transaction. If you must buy euros in London try http://www.bestforeignexchange.com/index.php They may beat the rate you pay using your debit card to withdraw euros in the eurozone.

I think you will find that those ATM looking gizmos are actually well concealed foreign currency vending machines run, at huge profit, by foreign exchange companies like Travelex. There's one in the waiting room for the Eurotunnel at Folkestone, too.