4040 HF5 is what you want. Axeon are a good manufacturer. There are a few cheap chinese copies floating around on ebay etc, I've no idea if they're any good or not, but personally I would stick with a reputable brand.
This is a "low pressure" membrane, ie it will work fine with normal tap pressure, as long as it's not stupidly low like 20psi or something.
You'll also need the CHAMP housing to put it in, plus a few connectors and bits. And, you will also need prefilters to protect the membrane, but they are cheap. You'll need a 5 micron filter and a carbon filter, with atlas housings for each of them.
So in summary you will need:
40 inch champ housing (about £180)
HF5 4040 Axeon Membrane (about £260)
5 micron filter (about £5)
carbon filter (about £5)
Atlas housings for the prefilters x 2 (about £30)
Connectors £???
As long as you change the prefilters every 6 months, and flush the membrane for an hour once a week, it should eaily last you 5 years.