Not sure when you're on route, but Dorchester Art Supplies has a range of model kits and pretty much everything art related (Decent brushes for one thing) Worth asking if you are after something obscure that's vaguely art/craft related because it's a bit of an Aladdin's cave.
Salisbury is not a bad model shop, but didn't find much WW1 aero when I was last there - good selection of paints and other modelling stuff though
Paul