I thought that I was using the official online booking service. Beware! Go direct to the DSA to book your test, this lot take £18 booking fee even though the DSA don't charge ANY booking fee. I've just been stung and i hope you don't get stung too!
If you try to cancel with these guys to book yourself they then charge a CANCELLATION FEE to the same value, daylight robbery. They should be shut down.