Latest TV report I seen suggest that the bombers might indeed have bought branded stuff from the shop floor, not some household chemicals over the counter. And it looks like you're stuggling if you want to buy old-fashioned chemicals from a Chemist, and as mentioned before it won't be long before the permitted list is reduced to mineral water (about 5 grams).
Egremont
BTW I'm reliably informed you would have been able to get Meths from a Chemist a few years ago.