Fortunately there was warning as it's been clear for a week or so that it was coming loose.
It's a glued in type and the black backing paint on the back of the glass has just peeled off and remained attached to the carrier.
I've found a couple of threads on similar failures but in their case the black paint had remained in place and strong double sided tape had effected the repair.
I'm quite happy with the idea of the tape (double sided vinyl floor tape) but I'm not sure whether it will stick effectively to the glass on its own.
Thanks for any help Rob