Got my car back, it's going to be a CAT S, got a very reasonable offer from the insurance co for writing it off and the salvage price was fair as well. As I need to get a new MOT with current insurer before it can be reinsured with them they stopped my policy.
Went online to another major insurer and got a quote there as they don't have any such requirements just that it has a valid MOT and having a car declared a CAT N or S doesn't void the MOT. Declared the at fault accident and my insurance came out cheaper than it was with previous insurer, grand total of £160 (one hundred and sixty). Noticed this insurer asked about the type of claim and date but didn't ask about value of the claim, I expect that is obtainable from some database.
So, got my car back, a few grand in the bank and going to see about getting it fixed now, if it turns out it needs more than first thought I can always scrap it and get the value of the salvage. As I planned to run the car until end of life any hit to future resale value doesn't really bother me but having done the numbers I think I've done alright.
boot floor looks perfectly straight as they left the plastic panel off when they dropped it off so that seems to be ok, panel the crash bar attaches to is pushed in a bit on one side but that can hopefully be pulled out as it's nowhere near as bad as some of the videos I've watched on youtube with similar damage.
As I don't urgently need a car it seemed like a good opportunity to try something a bit different.
Insurance company haven't asked for the V5 yet though which looks to be a bit unusual but it's taxed, insured and MOT'd so I'll look into that a bit further.