Like you, when i applied to uni i was desperate for a single room... however i applied late for accomodation and I am now staying in a double room... It turns out that i ended up with a double room and actually if i had my time over again i would apply for it again, main bonus is that is so much cheaper. I have no problem with it at all (other than i am not allowed onto the balcony that looks towards UCL main quad).
It really is the luck of the draw upon which single room you get some are small, as you say my beautiful aliel, however some of them very big.
If you want to get into Ramsay you should list your main priority as location - you want to be close to uni. If you do get into ramsay it is more than likely that you will have a single room. Also if there is any preference for catered or self-catered make sure you put down catered. Good luck