I've had problems where I've been staying in two or more hotels on the same trip in the states.

The hotels block off credit at check in, and then charge my credit card on check out. However, the blocked off credit is not released until several days has elapsed (sometimes upto 14 days!!). This means that you can have the charge for the hotel plus the blocked off credit appearing against your card at the same time. Do this at a couple of hotels in the same week, and it is very easy to exceed your credit limit.

This may be just a quirk of UK personel credit cards which don't have the limitless lines of credit like a company card.