I finally bit the bullet to replace the exhaust. The back box has had a hole in it for a couple of years and I have patched it a few times and it got through the MOT last year, but as its coming up again and the weather has been good, (working on the drive) I decided to go for it.
I had bought a new back box, a new cat, as there was no way the old nuts could even have a socket bashed on them, in fact the flanges were disintegrating, gaskets, stainless nuts and bolts and even a new sensor, what could go wrong?. The answer, just about everything. I had to use an angle grinder, drill, hacksaw and brute force to get everything off. When I eventually got it off, went to fit the new back box, which I got a couple of years ago, only to find that the left hand bracket had been welded on incorrectly. Havent got the receipt anymore so not sure who I got it from, so then spent the next few hours refashioning the bracket. Was dark by that time so now car sitting on drive waiting for me to refit everything, fingers crossed nothing else goes wrong.