If you bought the pads and nothing else, they should be under the allowed limit for duty (£18 I believe) as the exchange rate should make them around £12-13 and you won't be charged anything.
I bought custom shields and a spare cable with mine, so I might get fees if customs decides to have a look at the package. The annoying thing is that the duty won't be very much, but they tack on a handling charge for collecting the fees which is often more than what you owe the taxman!
I paid for the tracked priority international shipping and it looks like my package is on its way to the UK now. Hope yours arrive soon.