Hundreds of paramedics, firefighters and police are taking part in a simulation in the port of Dover.
Crews will be cleaning up a simulated chemical spill from a lorry which has accidentally dropped its hazardous cargo.
Officers are keen to stress that this is an exercise so residents should not be alarmed if they hear sirens in the area.
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The Transport Select Committee says the government needs to demonstrate that a lorry park will be the best solution for Operation Stack.
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Tuesday night's forecast for the west of the region