RE: The woes of a single man...
Yes, this has probably already been discussed elsewhere.
But anyway... i'm assuming London is not your home town, so you can't call old girl friends (as in the "only friends" part) and try to remember old times. Or something.
(if it is your hometown, then what are you waiting for?)
So, I'm thinking you actually are only WORKING there. I can totally relate. I lived for 2 months (only 2 months!!) in Scottsdale, AZ and well, I had 10 hour work days and almost no social life. That sucks.
I think the main problem is that you're probably focusing too much on the "tactics" part of the equation, instead of the lifestyle. Definitively your lifestyle doesn't lead to meeting new girls (as you describe), so, why not change it?
I'm not telling you to quit, of course... but what about volunteering? Or maybe joining a class of something? Cooking? Some local college course? It doesn't have to be something really intense (though of course, the more hours you put into it, the larger the probability of meeting amazing people =))
Really, there are a LOT of places where you can actually meet new people (not just "cute girls") and develop relationships over time. I know because I didn't do it while I lived abroad, and I consider that a huge mistake. Though it wasn't that bad, it was just 2 months. But 4 years? No way.
So, want to get a girlfriend? Well, have a social life away from work!
Oh, BTW: I'm not suggesting that you join something just for the sake of meeting girls. Trust me, that's a bad idea. Instead, try to look for something you LIKE, and then, as a really nice by-product, meet your future girlfriend.
Sounds cool, right?