non-standard previous repair
welding in a narrow return / folded edge like that is tricky because the eges will just blow out every time you arc up
I would have either cut further back and welded in a new whole corner piece, either from a donor panel or by fabricating a new piece. OR weld in a wider piece to start with (so it can handle the heat) then cut it down afterwards
Getting the geometry right would take a bit of care and attention though (in terms of maintaining the 'shut' around the boot door) so it looks like instead of that they sort of bodged in a piece to the back side
depending on budget (and assuming the other side is probably in a similar state) it seems to me your best bet now is a new rear panel https://www.minispar...wer-half-mk2-on (or whichever one suits your model correctly)
bracing up and cutting that out will also give you much better access to repair / replace the back end of the boot floor . wheel arches look alright though to be fair, could be worse
Edited by stuart bowes, Today, 12:16 PM.