Aside from prices and selection (for some reason the number in USD is equal to the number in GBP for almost everything, even when GBP is 1.6-2.2x the USD), it's size and layout of stores and staffing.
There were two main kinds of stores -- pale imitations of Best Buy, Circuit City, and Microcenter (out in the suburbs/small towns) (which is ironic since those businesses have had serious problems in the US market now, too, 10 years later), and urban small stores. The smaller chain stores (Dixons high street locations) had very limited product selection and you had to wait in a queue to get a salesperson to handle your purchase, rather than staff out on the floor to push products (often on commission) and then take the purchase to the registers. The big stores mainly had cookers and other white goods/appliances, with really limited selection of anything tech. This was 2000-2002. EU stores were a lot better in my limited experience (NL and DE). The only way to actually buy computer parts was to go to fairly sketchy flea market type buildings or fairs, mail order, or a small number of independent shops (at least in London; never found anything outside London).
Staff were even less educated on products than at a Best Buy in the US today, terrifying. Even getting people to take a model number and look it up in their inventory system was a minor production.