To close this thread off:
I've just got the car back from my man up the road, took longer than expected because he caught the Covid bug and being a 1 man business (most of the time) he was closed so the car was 'quarantined'.
Anyway he did fix it without having to dismantle anything.
He made a template out of some thing mainly made up of lignin, (C31H34O11), to my non professional eyes it looked very much like a piece of old cardboard box 😁. He gave this to a mate, together with a piece of solid looking piece of shiny metal, who has a metal bending machine, the patch is 'U' shaped with a flange that is also welded to the side rail, for good measure. The repair is no longer shiny but a nice black colour to match the rest of the chassis.
While he had the car and as it would be up in the air I gave him some EP 80/90 and asked him to replace the oil in the gearbox & diff. They weren't due to be done but why waste the opportunity.
There was a young chap waiting with his VW Sirocco, so I did warn him that it does take Fabian ( the man) a long time to work on cars by pointing out that mine went in new for its first service and was just coming out 😁. It took him a couple of seconds to get the 'humeur Britannique'.
Thanks to all for your help
Right, what next?