Correct if they write it off as an economical write-off it will automatically be registered on the national Register.
In effect you buy the car back but have to have a VIV done to get it back on the road and it will be permantly marked as a write off in future searches.
I advised him to either get them to repair the faults or simply use the payout to find another vehicle......issue is what they reckon it is worth and what you can buy with what is left over after the excess is paid......not a great deal when the vehicle is 20+ years old.