Was called to a job in Newbury, where the tenant could not remove the key from his patio door lock when the door was in the locked position. This is quite a common occurrence when the cylinder gets a bit worn. The cam slips through 180 degrees and then does not line up in the correct position in the locking mechanism. The cam can be re aligned but once it has happened the problem is likely to reoccur so I would normally advise replacing the cylinder. This can reduce overall costs as new cylinders have a manufacturers guarantee so the problem should not happen again in the near future.