The new 2.0 DTi Astras are part of the force's plans to increase the number of Incident Response Vehicles (IRV) it operates and will be liveried in police colours.
Diesels have been chosen as part of an environmental policy run by the Metropolitan Police, which is also testing 20 Vauxhall Dualfuel Astras in a bid to help the environment.
John Paddon, deputy director of transport for the force, said: 'The 2.0 DTi has proven to be quick and responsive and will be replacing all our existing Panda cars over the next two years. It is already helping us to cut our CO2 emissions under Government and Greater London Authority guidelines.'
The fleet of Astras has added specifications to deal with police duties. These include heavy-duty suspension, brakes, upgraded electrics, reinforced roof and light bar for roll-over protection.