Good question, there are bound to be a good few, I look forward to the responses as I am a northerner that is a little less northern now but still far north of London
There's two in Earl's Court, both next door to each other in Kenway Road. Both do a buffet-style lunch & dinner. Both are pretty similar in my humble opinion. There's also one in Tooting, 913 Garratt Lane Kusinang Munti Restaurant http://www.kusinangmunti.co.uk/about_us.htm ... again buffet-style, and whenever I've been there I've been reasonably impressed.
Check out this website: http://www.london-eating.co.uk/cuisines/filipino.asp To be honest, I don't know any one of those personally, but they might be worth the try.
Great ive got to try this place to taste what im in for before i fly out in the new year, hope they do that kare-kare and halo-halo