I am having a problem unlocking a uPVC door. The key inserts and
turns as if it was OK but, at the point where I would expect the door
to unlock, it won't turn any further.
Is there anything simple I can try to get in?

We recently moved house, and one of the locks operates in a similar
way to your description - the key turns in the lock to the point where
it should "click" as it unlocks, but it seems to "jam" mid-turn.

Applying a little extra pressure while doing all the wiggling as
suggested elsewhere seems to do the trick though in our case, but it
does seem to take a disconcerting amount of pressure to do so...