Among many other US dealers who will ship to the UK, I will add my recommendation for LIGHTHOUND, all my orders from him have been delivered quickly, I have been informed of the items shipment date, and the prices are great. Shipping costs are reasonable, and are dealt with by an 'international surcharge' which varies depending on the item, but is right there on the web page to see.
Another dealer who will ship to UK is OPTICSHQ, and they do a CPF discount coupon code, in addition to offering 'special' prices for members (create an account, costs $5, which is deducted from the first order anyway). The only slight downside to OPTICSHQ is that international shipping is not laid out on the site, it is calculated after the order is submitted, but Mike at OPTICSHQ will give a shipping quote on request, I got my M4 from there, and shipping was around $24 for Global Priority.
As I am in the RAF, I can get a 'military and police' price for Surefire stuff from Edgar Brothers, the imprters, but I still find, on many SF items, it's cheaper to add the postage, and buy from USA, generally LIGHTHOUND, especially batteries, where I am getting packs of 50 Battery Station lithiums.
Good luck !
PS, I just had a look at the STREETGADGETS website..... SF brand lithium cells, £11.98 ($21) for 2 cells !!!:thumbsdow I understand the markup needed for overseas dealers, but I will vote with my feet (and my money).