Having mentioned one online shop, I think I should go through a few others for British modellers.
I’ve used Hannants a few times and never had any problems with them. Good for military, detailing resin and Eastern European stuff. Not much for the car modeller though.
I haven’t used any of the following sites, but they’re bookmarked because I expect to one day.
DJ Parkins Home to four different lines, Flightpath, Firing Line, Great Little Ships and Modern Motive power providing kits and detailing sets for aeroplanes, military, large scale (specifically the 1/72nd Flower class corvette) boats and railways.
Scale Link An incredible range of military and railway related kits. One of the more comprehensive sites for World War 1 subjects.
Frontier Models Another source for figures. Not as comprehensive as Historex, but covering more of the areas (Film, TV, fantasy related) that I’m likely to be interested in.
Modelsforsale.com Mostly mainstream stuff but one of the better shopfronts I’ve seen.
Net Merchants Again, quite mainstream. There does seem to be a good selection of cars on this site.
Langley Models A large range of products for the railway modeller.