I have a premonition - I see a new fridge/freezer in my immediate future....
To put that off as long as possible (It's not even 17 years old yet - by about 4 months..) - do we have any appliance engineers ?
The compressor and all fans are still running, and it's cooling, but only to abut 12degrees. I don't want to spend £60 on an engineer callout if all he's going to say is it needs a new compressor.
Thoughts on what I can check please?
To put that off as long as possible (It's not even 17 years old yet - by about 4 months..) - do we have any appliance engineers ?
The compressor and all fans are still running, and it's cooling, but only to abut 12degrees. I don't want to spend £60 on an engineer callout if all he's going to say is it needs a new compressor.
Thoughts on what I can check please?

OMG our FO, Big Yank FF is approaching terminal time too, as it's16 & 1/2 years old .
It seems like your FF is dying or dead as both compartments are the same temp.