I just always get things that say "mum" on them, or "cheeky monkey" or are fun things like Peter Rabbit, Paddington, Highland Cows, anything with "haggis" (amazing the number of books/stuffed toys, etc that have haggis as a character), Loch Ness monsters, British play food (i.e are like fish fingers, heinz beans, etc), phone booths, double decker buses, In the Night Garden, Peppa Pig, Post Office/Royal mail, etc...
I think its so much fun to try and see what I can find that's British or has the 'inclination of being so'
Have fun shopping!