Apologies - I thought the thread had died and never saw the notification.
Thanks so much for all your help!
The knobs are 36mm in diameter.
Am attaching a pic of radio part it connects to, it appears to be press on (but may have been attached using glue as some of the know stayed attached when it broke).
I can see very small text on the second (Change) and third (tuning) knobs alright. Now maybe the others are replacement knobs already if they don't have writing on them, I don't know.
But certainly if anyone has one they'd be willing to sell I'd be delighted to get one.
Apologies again - wasn't trying to be rude!