Try Mainly Models in Hitchin for kits.
Nearly all the combat flown in the UK is 12th scale. If you do not have a lot of experience with small fast models, the Hurricane is a good first model and is a frequent winner. The Hellcat with a 25 is also good.
Do not be put off by the foam brown paper construction. Just follow the instructions. The combat guys are a very friendly bunch and will help out.
Here are useful links
http://www.geocities.com/capecanaveral/runway/9790/ UK COMBAT HOME SITE
http://www.mainlymodels.co.uk/index.php?cPath=23_120 BEST UK COMBAT KITS Hint make drawings of the bits! Cutting foam is easy.
Combat is great fun and the models are good sports field models.