if the police are not doing anything about it .. then go to the police station and shout at an inspector untill someone does do something about it... yes you do have the right to speak to one...
there is no reason the sgt should not deal with it, no matter what history ythere is.. if you feel this is the case then make a formal complaint to the ipcc..
firstly about the fact its been reported stolen and secondly that fact nothing has been done about recovering the car...
http://www.ipcc.gov.uk/en/Pages/default.aspx
if you have reported it stolen the police have to act upon it and recover it ....