Do you have your heart set on using the official Warhammer(tm) miniatures?
Because you can play the Warhammer game with whatever minis you want. As long as the minis are about the same size (25mm scale), they'll be perfectly useful with the Warhammer rules. Sure, the official Warhammer minis are really nice, and they're specifically made for the rules, but they're also pricy and time-consuming to paint. (Paying someone else to paint them for you is even more pricey!) There's no shame in using cheaper substitutes as you build up your official collection over time.
If you're just playing among friends, you could even use those green plastic army men that you can buy in a discount store for a pound-a-pack, or maybe even less.
But it's kind of surprising to me that you'd have a hard time finding Warhammer minis in the UK--isn't Games Workshop a British company?