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Update: Thankyou to jno for providing the link that eventually partially solved the problem.
Firstly I realised I no longer had the System file 'Screenshots' in my library. I then realised that I'd probably deleted it by mistake when I transferred a batch of photos into a different location. Apparently you can't just move THE screenshot file to another location you have to create a folder then move it to the folder otherwise it deletes itself.
I found out from the link that Windows creates a Screenshot file when you first use the Windows + prt sc button and if you inadvertently delete this file you can create a new one by going into the RegEdit , finding the DWORD value Screenshotindex and resetting the Screenshot sequential numbering back to 1.
I've done this and low and behold the ScreenShot folder is back in the libraries.
The issue now is that although I now have back the Screenshot folder in the library, its empty, and any screen shots are still going to the clip board and not the folder