As said before, when my Omegas rust I scrap them. There are still lots on e-bay and elsewhere, find one to your taste, look at rear wheel arches for rust, and buy a better one.
As another thread relates, this year I hope to get 8 cars through the MOT. To avoid unnecessary failures, I check the next due car for exhaust and tyres early to enable relaxed replacement, then pre-MOT it a week before test, then final examination, wash & tidy on morning of test day.
Be ruthless, Kate, look around for a better car. There was a 2001 manual 2.5CDX petrol saloon on e-bay 2 weeks ago, MOT till December, for £450, which then dropped to £395. I wanted to buy it as a spare, but the wife restrained me. There are still bargains about. Your being in Cornwall might make collection expensive, but regard it as a day out. Last year I bought a car in Plymouth and another in Clacton. Who needs holidays?