can i get the car taxed and insured again myself, or does it have to be him? even though the car isnt being used and is sitting in the car park of my flat? can that be classed as SORN or does it have to be in a driveway?

If it's not on a public highway (thus on private ground) then you may declare a SORN otherwise it must be taxed and anyone may pay the tax as long as they have the insurance cert and MOT (if applicable).
Unless the car is inaccessible to the public you should speak to the insurance company about insuring the vehicle against theft and damage by vandalism or attempted theft but I would advise you get someone to immobilise the vehicle anyway.

Contact the DVLA and his insurance company so you can be advised of the correct procedure. If the car is not parked on the public highway it should be declared as such to the DVLA so that you do not pay road tax. Best to keep it insured in case any damage occurs