Just to update on this situation, after reading several other reports like this on various forums I decided it was time to call Apple support again. It appeared some owners were getting easy replacements and others were being told no.
I spent around 20-30 minutes on the phone initially with a first line support agent and then a senior advisor. The latter was very patient, helpful and knowledgeable and immediately agreed this should be a straight forward replacement, no question. They went away to discuss with a colleague and to authorise this, normally I believe they would require the broken strap to be returned for analysis.
Around 5 minutes later I received a call from the same senior advisor who informed me they would be sending a replacement solo loop without the need for me to return my existing one. This time around it was a very pleasant experience on the phone to support.
So it would seem if you are not happy with the initial outcome then jump back on the phone. Push to speak with a senior advisor or member of staff who should be more accommodating.
As the advisor pointed out, this could have been a more unpleasant outcome if the watch had fallen onto a hard floor when the strap failed 😲 - this could have lead to a much more serious replacement situation, certainly food for thought. I do hope that others aren't unlucky enough for that to happen.
Anyway, I will await arrival of the replacement solo loop and give its owner the good news 😊