All_Fours wrote:
if it's been written off, you'll probably need to get an engineer's report for the crash repairs, otherwise you wont pass the compliance test
Exactly.
When it been written of you need a repair cert for it.
That means that it is inspected in damaged condition and the inspectors says that that and that need to be replaced.
If it has a damaged chasssis rail or similar and he says it needs to be replaced, it's either replace it or scrap it, there is no other option.
You cannot choose what parts to repair, and it needs to be done properly or it will need to be done again when they re inspect it after copmletion.