Also, make sure you renew it using the company that sold it to you.
You will probably get a letter in the post from Nominet (the body that issues the domains in the UK) who will offer your a chance to renew it for a hefty fee much greater than the company that sold it you. There is a good reason behind this, if the company that sold it you for some reason or other doesn't offer you a chance to renew it or disappears since the time you bought it then they make sure your able to renew it but their administration fee is quite high.