Couldn't quite believe it but Franprix has a quite a few English products on a rack in their shop in Evian, including HP Sauce, Lee & Perrins, Heinz baked beans, and Cadbury milk chocolate. Pretty good prices too. The shop itself is at the former Marché U which you can find in Google Maps quite easily, just five minutes away from the harbour (I go there by boat). With the Euro so low, it's really convenient and this stuff is an extra bonus!

You'll find the same closer by than Evian.
Take the highway exit of Coppet (LNN to GVA), take a right and straight through to France.
Just across the border. on your left, there's a Casino supermarket (open on Sundays until lunch) with lots of British products