There are other threads on how to do it, I will look to see if I can find it, but it is there somewhere.
I always pay in cash, but I believe you can use a card, but I think that would be more hassle. I think you could pay in US dollars, not sure on pounds.
edit, this is from another thread:
Getting an extention visa is so easy. You do it on arrival in manila. Line up in the immigration queue as normal, when you get to the officer, tell him you need a longer visa, he directs you to the door on the left. You go in, tell them you want to extend, they get the ok, you pay, then go back to the immigration line and wallop!! you get your stamp. I have done it a couple of times already. No hassle.