How long are cheques valid for?
Banks will usually reject cheques that are more than six months old but, in fact, it's at their discretion. They can choose to cash it if they want to so don't assume that if you wrote a cheque to someone over six months ago that you're off the hook from paying it! Cheques actually remain legally valid for six years - yes, I did say six years - and the only way to cancel a cheque is to ask for a 'stop' to be placed on it. However, cheques backed by a cheque guarantee card cannot be stopped.
http://www.lovemoney.com/news/current-accounts /your-essential-banking-guide-1029.aspx