If you are concerned about fitting, buy a JTE! They are adjustable at the back so fit any size head! My head is a 6 7/8's but iv also had a 5 year old wear it aswel as someone with a bigger head, it is the juniour one which is about half the price but will fit most adults before you are conned by some shop assistant to buy the adults one lol

According to the AA website you live 25mins from me and there are loads of riding schools around here!! Try Cobham Manor,The horse Sheos, Callum Park Riding Centre, Go on to the BHS website and look up all BHS registered riding schools. Seeing as I am the other side of maidstone to where u r I would suggest Maidstone is your best bet and also Aylesford, Chatham etc
I would definately recommend the Horseshoes though, I know alot about there and they are a good place to start!!

Good luck!!