Mila brand lock on windo wont open

[fitzykev]

Moved into a new house and the lock on window is mila, the key turnes in it and when you open it the left side seems to stay locked but ight side seem to loosen. Any ideas?

 

[crank39]

It pressumably then has shootbolts to the left and right and the left side is staying engaged so sounds like a centre gearbox failure, to open you'll almost certainly need to remove the glass and then bend and fiddle the opening sash open levering it sideways so the shootbolt comes out of the keeper on the frame