Hi Venom
I don't know anything about UK but what you need is like a football or soccer feild or even a baseball feild, that would be plenty of room for flying the cub or average park flyer
If there are any that are for public use that would be the way to go, you just have to watch for fences when flying low
or find someone that has a cow pasture and ask them if they mind letting you use a corner of it
I fly in a feild that is where they hold carnivals
Just some ideas
Good luck

Edit:
Venom I just remembered I think there are a couple guys over on the park flyers forum from the UK
You will find more responces there than here anyway