Ozzie,
Yup, you're right. Bought a pack of Araldite Rapid, (... cures in ~15 minutes), stuck a big blob of it to both sides of the broken plastic mirror support and so far, it has done the job.
What amazes me, is that the repeater indicator light still works AND the electric motor to drive / adjust the mirror works too!
So, thanks for the suggestion.
It has allowed me to drive the car short distances without the police interfering.
The car is being removed tomorrow for the rest of the damage to be repaired, I hope.
Pat Jeater