I want to know how to replace a lock that is in a (unlocked) uPvc door.

The word Yale is on the lock, it is probably eleven years old, and from what
can be seen of the lock whilst it is in the door, its shape looks like a
standard Euro profile cylinder lock. It operates top-and-bottom shootbolts.
Protruding from the door edge is a small triangular cam which engages on a
striking plate on the door frame. When the door is closed, this triangular
cam is depressed, releasing the door handle so it can be lifted upwards to
position the shootbolts (the cam mechanism is very difficult to get to work
at times).

However, there is no long screw at right angles to the lock, holding it in
place, as might be expected with a current Euro profile cylinder. There is
instead a hole in the door frame where the long screw, if there was one,
would go through. At the bottom of this hole I can just make out parts of
the lock which rotate as the door handle is rotated.

Can anyone identify this lock, and tell me if it can be replaced with a Euro
profile cylinder, and how?

(I have asked Yale but so far have had no response.)