Parkers has a 'straight' one at about £1500 or so
http://www.parkers.co.uk/cars/prices/used/vauxhall
Rumour had it a few years ago insurance companys only payed out about 1/2 of the value of the car to a cat c/d if it was written off again.
As you say he repaired it himself its hard to know how well the repairs were done, if he just used a cheaper garage then dispite its history the car could fetch close to the parkers guide, if a cheaper home/bodge repair then maybe not so much.
I would definitly advertise it saying 'previous cat c/d (whichever it was)' and if it hasnt been done before then it will need a VIC check done by the DVLA
https://www.gov.uk/vehicle-identity-check before they will release the V5 to a new owner so if its done before its another selling point that the repairs have been done.
Even if no repairs were done then crash damaged auction houses sell damaged cars a lot more than scrap value.