Can Anyone Identify This old Lock? Post your questions and get answers concerning many areas of this subject

[Rosie Rabbit]

I am trying to unstick sliding patio doors that have been locked up for years. I've done the wd40 and the graphite powder thing and the main lock has freed up but this little devil which is at the top of the door and bolts into the top of the frame will not unlock. I can get the key to turn back and forward but I suspect it should be going further to the left to release the bolt. Have tried pushing, twiddling, hammering the frame etc but to no avail.

Has anyone got experience of these old locks, what are they called, how do they work and how to get the little so and so off if it's banjaxed. Any help appreciated before I have to call the big boys in.

Thanks

[Rosie Rabbit]

Just an update on how I got the doors open. Having thrown every lubricant known to man at them, I took a rubber mallet to them and banged all round the frame. Must have dislodged something, because they just slid open like a knife through butter. The joy was boundless.