This is the undercover emergency police car that Frank Carter drives a lot. Although it comes in silver, it has blue sirens; thus being an undercover car and having the exact same body type as the police Vauxhall Vectra. The purpose of the undercover police car is to make it look like a normal Vauxhall Vectra and to not draw attention to any gang member.
Clive McCormack drives two Vectra's. One is the same as the one Frank drives, the other however is the exact same car but it's colour is red. This particular version is only seen in the mission: Stalking McCormack. The player is able to get into this car and drive about, but only when McCormack leaves it to enter the depot.