You would not enjoy dancing in most of the London milongas unless you know people there already and are content with dancing within that group for the whole night, with maybe one tanda from a leader outwith. However, as
@TTanguero might recommend, there are milongas within and in the vicinity of London that you would probably enjoy a lot more:
Pavadita in Hammersmith, organised by Nikki
Tango Café in Clapham, organiser by Katerina
Tanguito on Tuesday nights and Sunday afternoons, organised by Bruno (Actually, not so sure about this one)
Further out:
Cambridge on Tuesdays and Fridays
Thames Valley Tango at Old Windsor and Basingstoke, organised by Charles and Sarah
Tango Secrets at Maidenhead, organised by Irina
I will also tentatively recommend the Spitalfields outdoor milonga, organised on one/two Sunday afternoons a month during the summer at Spitalfields market, if only because essentially everyone goes there, the atmosphere is great, and I think you have a chance of getting dances, but given that it's very, very well-attended, getting lost in the crowd is a definite possibility.
I will not recommend Tango Garden on Saturday afternoons because the attendance (I hear) is not good.