I have had trouble with gaining access to a couple of bookies (namely Expekt and Bluesquare) using a USB mobile broadband (Vodafone) on my Mac. Finally I have found a solution and thought I would post it here just in case anyone else comes across the same problem.

To solve it just download some freeware called ByteMe Optimizer at aitne.com. Doesn't seem to do much when you run it but it solves the problem.