There's huge money to be made from BTL in London, although it's far more a long term investment, than a straight out money earner.

I would only BTL as an extra on top of a regular income, as you'd have to have a huge number of properties to make it worthwhile. Having said that, I know a couple of people who have done exactly that, and with the ridiculous capital appreciation on the large number of properties one of them "owns", it's certainly not been a bad few years for him.