Si, Just seen this, Sorry to hear all the aggro
Have you accepted a figure in full settlement for your 90 ?? If not, the vehicle is still your property, while a insurance claim is going through,
The garage in Sussex has not done their "duty of care" in looking after your property,
How it normally works, is that the insurance company want to minimize their cost, firstly by using a salvage company to remove the vehicle to cheaper (read free) storage for them, The Sussex garage should not have released the vehicle without your permission, even if it mean they would start charging you storage !!
The garage could not refuse you access to your vehicle, because as otchie1 states, they could not hold a Lien over your vehicle, as no improvement has been done to it,
When the vehicle is finally declared as a write off, then yes, a private individual would have difficulty in retained the salvage, due to being classified as waste, The insurance companies have to be seen to be disposing of their waste as per environment agency regulations,
If your are claiming the winches, tyres and diff-locks etc, If and when they do pay you out for them, they have to stay on, as they would then belong to the NFU
IMO the problem lies with both the NFU, for instructing Hewitt's to remove the vehicle (especially as you refused consent & the garage for releasing without the owners permission, )
Best of luck mate, give them stick