Thank Steve for that!
A lovely lovely man from Apple just phoned to say my Mac’s back in the land of the living.
Thankfully it was just the graphics card which had failed and so they gave me the option of paying for a service replacement part of the same model I had in there, or an extra tenner to upgrade to a significantly more spangly bang up to date one. No charge for the repair either way.. Hmm, let me think?.
Suffice to say I’ll just pick up a new card in the morning and normal service will be resumed.
Phew, he says breathing a huge sigh of relief. I’m a very happy chappy now :-)