The vast majority of BT contracts do not auto-renew. At the end of the minimum period, they simply turn into a rolling monthly contract. So you don't actually need to do anything, just contact BT a month before you need to terminate the contract.
Avoid signing up to any new service or accepting any free new equipment, as this may renew your contract without you realising it.
There is one thing to worry about though.
If you cancel the broadband in or out of contract, there is a £30 charge to pay. This charge is levied on to all ISP's and is passed on to you the customer for the work done to disconnect the broadband at the exchange.
If you were transferring your broadband and used a MAC code this charge would not apply.
I am not worried about the charge. However, I am worried that it is mentioned that not all contracts do that! Think I will call them, preferably when I am in a very stunning mood so that by the end of the call, I will only want to maim and kill and not be suicidal. Thanks for all of your advice.