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I've Fixed it!!
set about things this afternoon, took every single visible screw out around the general area. Was unable to remove the side panel, but from the back, once the back panel was off, I could see the offending back plate & as Mother Nature blessed me with hideously long arms, I was able to reach in & hold it in place whilst the hinge was screwed on from the front. Hurrah.
The bottom one was altogether more complicated, as i couldn't reach in far enough, due to all the insulating foam & the actual oven.
Hmm. What would Macgyver do..?
I had a telescopic magnet which I was able to poke into the gap & sufficiently hold the back plate in the general area, until, from the front, the screws bit & pulled it into place. Again Hurrah.
It sounds all quite simple, but it took AGES & a few profanities.. but I did it, it's back together & all works. Am proud. Thanks to you all for your words of wisdom & support.