The police overtime bill for Operation Stack was more than £625,000 in 2008, the Kentish Express can reveal.

The figure was five times as much as it was three years ago, figures obtained under the Freedom of Information Act reveal.

Stack, which is brought in when bad weather or industrial action blocks the Channel ports causing a backlog of lorries that have to be “stacked” on the M20, was implemented 21 times last year and cost £625,309 in police and support staff overtime.

In 2005 Stack was implemented 18 times and cost £123,000 in overtime.

The statistics may state that Stack was only implemented three more times last year than in 2005, but 2008 was a particularly dramatic year.

In February and March, motorists suffered 17 consecutive days of misery when SeaFrance workers went on strike. Then on September 11, fire ripped though the Channel Tunnel, causing massive disruption.

Stack puts huge demand on manpower. Phase one, when the motorway is closed between junctions 11 and 12, requires one sergeant and 21 police constables.

Phase two, when the M20 is shut between junctions 8 and 9, requires two sergeants and 28 constables.

Kent Police had to call on other forces, especially Essex, in order to staff Stack, and the officer overtime bill of £609,944 includes those costs. In addition, there is a £15,365 bill for support and administrative staff. Figures obtained by the Kentish Express under the Freedom of Information Act, also reveal the meal and refreshment bill for Stack was more than £15,000 last year.

The total policing cost of Stack to the taxpayer in 2008 was more than £700,000.

In a statement, Kent Police said: “2008 was an extraordinary year which saw extreme weather conditions, berthing problems in Calais, industrial action and a fire in the Channel Tunnel, all of which created congestion and the need to implement Operation Stack.

“Kent Police is working with the Highways Agency to discuss the best way in which Highways Agency traffic officers can work with our own traffic officers, in addition to the improvement of signage and road layout to assist in implementing Operation Stack.”