Operation Stack: Ferry and rail services suspended at Calais causes standstill on M20

The port in Calais is expected to remain closed until Thursday after picketers burned a tyre barricade, blocking the port entrance

Operation Stack: lorries queue at the port of Dover on 23 June as workers blockade port at Calais in France (Carl Court/Getty)

Striking French ferry workers have shut down the Eurotunnel causing chaos for the second time in a fortnight. The strike has caused chaos in Calais and gridlock on the main motorway that runs through Kent and is used by lorries wanted to reach the continent.

Kent Police, who warned motorists of "significant disruption" to their journeys, said phase two of Operation Stack had been put in place on the M20 southbound. The operation is renowned for causing mayhem for those who need to use the motorway - and leading to long snaking lines of lorries that stretch for miles.

What is Operation Stack?

Operation Stack: lorries queue at the port of Dover on 23 June as workers blockade port at Calais in France (Carl Court/Getty)

Operation Stack is used to park lorries on the M20 when Channel Tunnel services are disrupted. Lorries travelling towards the continent are queued along sections of the motorway to avoid blocking roads across Kent. There are three phases of the operation – phase one which closes between junctions 11 and 11A, phase two which closes between junctions 8 and 9 and phase three which closes the London-bound motorway between junctions J9 and J8. The policy often causes widespread disruptions to non-lorry drivers also.

When is it used?

Striking workers from My Ferry Link light a tyre fire to block access to the Channel Tunnel entrance in France on 23 June (Philippe Huguen/AFP)

Operation Stack is used when circumstances such as industrial action, fire, accidents or severe weather cause Channel Tunnel services to be suspended. In the first 20 years after it was implemented in 1987, it was used 91 times. Parts of the M20 are currently in gridlock under Operation Stacks. As a heatwave is expected this week, Kent Police have issued a notice to motorists advising them to keep water in their vehicles and not leave young or elderly passengers in stationary vehicles.

How is it enforced?