I have been part of car clubs for a long time and although I'm not a highly active member on here (but should be), I appreciate the good advice, always! I completely trust everything you lot are saying. I'd already read up on it and just wanted to reassure myself really before challenging a mechanic. My hesitation is more of what to do with the MOT tester aside from proving them wrong. It's just a bit complicated although I am p***** off I could still come away from this with a hole in my car to patch up instead of rust that was at least giving some protection to the bits behind it. I may just have to live with the fact that I need to repair those sill panels anyway so a hole isn't going to make much difference, especially if I just replace them.@NickUK a bit of context for you as we're possibly starting to look like a lynch mob for the businesses involved here.
There's various pet subjects on here and MOT fails on sill covers are one of them. It's a fairly clued up bunch on here and we've also got a couple of current/ex MOT testers. So views are firm on this.
The technical advice you've been given is correct. But do your own thing with any follow-up action - no one is going to judge what you do or don't do there. It seems an obvious mistake to make to me. But then I'm always banging on about how ruthless the tester is at my garage. And for reasons that suit me I still go back there.
I'm driving the car across to the tester in a few hours so he can "show me" that the sills are part of the structure. I will then show him he's wrong