o.k nicola is your rear door wooden? If so its quite easy what you need to do is plane a little bit of the top of your door where it is catching you may need to take the door of. if this job sounds a bit to much it may be eaiser to get a joiner round it should`nt cost to much either. make sure if you have ago yourself you don`t take to much of as you could reuin your door. Remember to prime any bare timber or your door could swell even worse. I hope this has been helpfull to you regards martin joiner/locksmith.
martin
December 2008