SOLVED Replacing cylinder lock, can't remove retaining screw

[gravesend46]

Wife's bag with keys and ID was stolen last night so trying to change lock on my uPVC door. Everything online makes it look nice and easy to remove cylinder retaining screw but mine seems to have some kind of barrier between the door side faceplate and the screw, preventing it from simply being unscrewed.

Can't see anything that would make it retract. Is the only option removal of the entire metal sideplate down the side of door?

Thanks!

 

[gravesend46]

Actually, ignore me. I fixed it after taking a closer look and realised it was part of the double-lock mechanism. If I 'unengaged' that, the retaining 'plate' moved aside!