B&H are happy to supply to the UK but require payment in full beforehand. That means that if you are using CC they request a full photocopy/fax of both the front and back of your card to verify you have it and they will only post to the address the card is registered too as well.
All vat and customs that you may get hit with is also the full responsibility of the buyer, as is the return postage costs should you need to send anything back to them for any reason.
I nearly ordered a lens from them and got up to the stage of CC verification, but as soon as they wanted copies of both sides I pulled out of the transaction. With that info anyone could order online from most places without a signature and I was not about to open myself up to that chance.
Since then OneStop has begun trading and offering duty free or refund should you get stung, this is a better option for most as its almost as cheap and less risky, as Dave had said though, a cheap weekend trip to the States would be a even better value as you get a mini break, chance to check the product when you buy and hopefully some great shots of NY while you are there
