6 unmarked police cars 2 bikes - what's going on

[ds666]

Travelling through Stourport tonight was passed by a convoy of 6 unmarked police cars and 2 unmarked motorbikes , at speed . At least 3 of the cars were e63 amg estates , one r36 passat , all with blacked out windows . I say police because they all had flashing blue lights ( in the headlights ) and sirens , no markings . What was happening ?
Theories on a postcard pls ..