Rover owners: Bodyshop so far (pics) + advice please!

Well the car is in the bodyshop getting fettled, as you can see below. However, there is some concern over the rear wheel arches on both sides - as ever! Due to the amount of rust, no guarantee of it not reappearing can be given, which I understand fully.

However, and this is where I need the help, can I source a couple of rear quarter panels and just get the bodyshop to cut out an inch above the wheel arches and weld into place?

THey were talking about fabrication of new inner arches. I don't really want to go tinkering with the whole rear quarter panels on either side, if as much for cost as well as structural integrity?

Has anyone done this? Is it indeed feasible? I can source a rear quarter panel (repro) for £195 inc vat.

Many thanks in advance.....