If you want Sussex area, keep an eye on area 10 and 13 websites, ardingly riding club, horsham & district rc, going & district - they normally do events at Ardingly/Coombelands.
If you go on pony club website there is a calendar. If you click on that it will list all the pony club events for the coming year that have been registered with pony club. If they are not there check the branches individual websites in your area and they will list them all.
Hope you find some to go to!
Hiya - September, Chilham park (they have a website www.chilhampark.com or co uk) ... not one to miss! they run BE too so the unaff one is super organised, very friendly, jumps are fantastic, its like a BE event but mini! I did it for the first time last year and came about 36th out of 90 entries in the 2'3 class and has such a fun day. Definately going again in '09, think it goes up to 2'9 , maybe a bit bigger