Shouldnt be a problem as long as you are returnıng before ıt runs out. They may check your tıcket to make sure. Even ıf you are returnıng to the UK after thıs date you can get an extensıon from the Brıtısh Consulate ın Portugal.
...or you could renew your passport early and get the extra months credited to the new one, so that it expires 12th Feb 2016. You are able to do this up to 9 months ahead of expiration.