Do it yourself
After reading around a bit I decided it was not too big a job. Covers are only held on with 7 screws, then three bolts for the motor.
Got it off and liquid metal'd the broken end back onto the link to hold it in place. Then I took three jubillee clips. Cut the screw off one just to get a strip of metal. Wrapped the strip along the link, round the end and back up the other side and secured it to the link with the other two clips. Got it tight as possible.
Have been using it ever since. Total cost of repair an hour and a half and £8.50. I should have taken a picture, but it was cold outside and just wanted it done.
Whilst I have no idea of the longevity of the repair, the price of a second hand wiper motor/links assembly is around £80 (Autolusso), so I reckon I'm quids in.
Thanks for all the replies and suggestions,