I think Jessops guarentee to match any local shop prices, but only internet prices at the managers disgression - and only UK based sites with UK stock, ie not Pixmania as thay are in France and their stock is all European/French rather than British.
I've never failed to get an internet pricematch, as already suggested you just need to be persistent if they try to argue. At the end of the day though, they have so many stores you can just walk out and find another store that will offer the pricematch.
Mark.