Hi, I went over to my son's house to do some gardening as he is on tour in Afghan. He has a upvc door and the key opened it fine. After gardening all day, I cannot lock it??? When the door in not closed properly, I can lift the handle easily so all the 'sliding' mechanisms work and the lock locks perfectly. When I shut the door, again I can lift the handle easily and it sounds/feels like all the sliding mechanisms are working, but the lock will not lock. It is just jammed. I have been trying to sort for an hour with no luck. Can anyone please help or cast any light on this??????? Many thanks.