uPVC lock filled with sticky stuff forcing it locked?

The key in my back door has been left in by previous tenants and was stuck in there. I managed to pull it out and it was very sticky and gunged up. By pulling the key out all the barrels of the lock have been glued in a position and now I can't unlock the door as they're not free to push against the key. I tried cleaning the key and putting some graphite powder on it and pushing this in and out of the lock but it hasnt unstuck it. I've also tried pushing each pin down with a hair clip to try and loosen them but this didnt work either. Any ideas?

Ed ML
February 2011