I'm based in London and frequently go into all the four conservatoires here. I'm afraid I have to report that, based on my meetings with pianists at (or recently departed from) each of them, and performance I hear in the colleges, Trinity seems to me probably the weakest piano department. Of course, if you have a specific teacher in mind that you want to study with who is there, that's a different matter. Or perhaps you think your chances of getting into the others may be slim, in which case fair enough.
Also London is a depressingly expensive place to live and study, and large and difficult to get around. I manage OK by cycling everywhere but if you live more than walking distance from college and have to use public transport every day you may well soon find you lose the will to live.