You can go to the 2 Malvern shows (Spring and Summer) and pay on the day. Although these are smaller than the other RHS shows they are my favourites, since the best nurseries attend them and persuade you to part with loads of dosh. I buy my summer plants at the one and my spring bulbs at "tother. Not sure about Hampton Court and have never been to Tatton. A phone call to the booking line should answer your Qn.