Carl,
I cant answer your question as I am not from that area but just wanted to say that the going rate for 1000 ltrs of water is no more than £25. try your local YP and ring a few w/c who use wfp.
Many moons ago (before we purchased our RO) we paid £80 a tank. Found another supplier at £50 and finally £20 from a reputable supplier.
Dont get ripped off. You can buy a small but adequate RO unit for a few hundred pounds.
Sarah