Have you considered promoting this via a FaceBook group?
There are two options - either the viral option of people encouraging others to join-up, this is very successful in driving traffic.
There is also the option to take paid advertising. A recent campaign we did got a great response rate. Probably best to message me directly if you want to know more, or want help setting-up as I don't want anyone to think I'm working for the website!
You'd also appear in searches whenever someone searched for "London" or "SE1".
Good to meet you, James. It occurred to me, on the way home, that I learned about the Colombo Centre through an ad on the back page of your Newspaper! So - thank you....for putting me through 3 years of toil, tears and sweat, lol.