Remarkably this year 2017/18 we have seen for the first time a lot of problems with uPVC doors. In previous years we rarely saw problems with these doors.
It is generally possible to adjust both uPVC and aluminium doors and we particularly like this little video which give a good explanation of how to adjust door latches. We would like to reiterate how important it is to ensure that the door still locks! Due to the fact that with uPVC doors the frames are made from plastic cheaper varieties can use screws that fix only into the plastic making adjustment difficult and if overtightening happens then larger screws may be needed, where the screws that hold the keep bar are housed into the plastic frame it is almost impossible to get satisfactory results. In theory it should be possible to get a new keep plate but in practice this is virtually impossible and fitting new lock mechanisms to PVC doors is really a factory operation and needs the frame in the factory too.
Here is a picture of a very high quality latch plate fitted to a wooden door, the keep is adjustable and the screws that fix the adjustable part of the keep fix into threaded tapings into the metal casting making them reliable and robust.