Thank you Liam. If you don't know a roller from a latch and you want to differentiate your specific uPVC door (or patio door - in our case) - or... know that Points A / B - are industry standard references - this was perfect.

Very clearly explained. Thanks Liam.

What about front doors that have automatic hooks as the door closes pins are depressed by frame which causes I believe spring loaded hooks to pop out into slots in frame door handle does not lift up the hooks retract using handle either side of door pressing down on handle retracts hooks and resets pins ready for when door closes again

Hhahahahah Chriseutosong you are right! LOOOL

I have a slight issue my latch bolt only works via the internal handle, it doesn't slide in when the handle is pulled up from outside. When closing the door from outside you really have to push it. I did a temp fix by removing the rectangle it goes into located on the strike plate. Is this a full replacement or can I fix it somehow? Also I'm tempted to grind a wedge/angle in the removed rectangle to aid the latch bolt sliding home. Any help is appreciated.