Hi JB and welcome

I think you're making things difficult for yourself if you only advertise on 'mainstream' sites like Gumtree; maybe less so with Vivastreet but it's very expensive and like the others will likely swamp you with timewasters to the point where you'll feel like giving up. I can't imagine that Twitter will get you actual work unless you spend a ridiculous amount of time on it and Google+ can be a downright dangerous tool if you also have personal accounts on it and don't make sure all the privacy settings are on. I'd recommend having a look through the Adultwork section here - it's certainly not the be all and end all that some would have you believe but it's relatively cheap and will at least get you some bookings.

As for London, there are lots of areas cheaper than Baker Street and surrounds - don't think you have to be in Zone 1, either! There are threads scattered around about renting and you don't say whether you want to live and work from the same place, but if you'll struggle to get references or maybe a guarantor could you just do outcalls for a while until you get some financial records built up? If you can do a good massage you should do well anywhere - it's a popular service and definitely in demand .

Echoing amy, AdultWork is a great start. I've got a couple of decent regs through twitter and lots of one off bookings, but like Amy says it takes a fair bit of effort and time to build up a social media presence.  I find anywhere near the financial district to be very lucrative especially for same day bookings. Good luck!

Ghostworld, the English school holidays don't start for approximately another six weeks yet. At the end of July.