Just thought I'd let you all know, if you want some Ali sheet at the moment, Industrial Metal Services (IMS) in Essex were the cheapest by far.
For: 1 off 2mm 8 x 4 NS4
2 off 1.2mm 8 x 4 NS4
Parkers - £205 inc vat
SPA - £147 inc vat
Aalco - £151 inc vat
IMS - £110 inc vat!
These are all based on collection.
Hope this helps someone, IMS are nice guys to deal with, and if you need delivery it's £25 + vat