The government is refusing to say how much taxpayers are paying to keep the former Manston airport site on standby in case Operation Stack is implemented.

The site was chosen to be an emergency lorry park in August last year after several weeks of disruption caused largely by migrants breaching security at Calais as hundreds sought to cross the channel illegally.

But Manston has yet to be used as measures taken by the government and Eurotunnel to boost security have succeeded in dramatically reducing the efforts of migrants based at the Calais camp to reach the UK.

Despite this, the site will remain on standby at least until June, when the contract between the DfT and the owners runs out.

The Department for Transport has rejected a Freedom of Interest request made by the Thanet Extra to detail any of the costs associated with the use of Manston as a relief lorry park.

It says to do so would prejudice the commercial interests of the Department for Transport as it sought a permanent emergency lorry park.

In a letter setting out its reasons, the DfT said: “The arguments against releasing the information is that the information is a matter of commercial confidentiality whilst the Department and other parties are involved in obtaining a longer term site to be used as part of Operation Stack.

"The release of the information at this point in time would be prejudicial to the Department for Transport in obtaining a long-term solution that provides value for money as its release would put us at a commercial disadvantage in negotiations.”

It added that the contract was “continuously reviewed”.

In August, the airfield was equipped with floodlighting and lines were painted for spaces, while caterers, round-the-clock security staff and parking marshalls were contracted.

Toilets and shower blocks have also been put on the site. However, the site has remained idle since August.

Owners of what has been renamed Stone Hill Park have had a contract renewed until June but it is not clear what will happen beyond that.

There has been criticism of the decision to use Manston as a relief lorry park, with North Thanet MP Sir Roger Gale describing it as insane. South Thanet MP Craig Mackinlay saying he hoped the arrangement would end soon.

The government has backed away from reforms to the Freedom of Information Act, saying the legislation is working well.

There had been fears that the government was considering introducing charges for requests. Thanet council was among public bodies calling for fees to be brought in as a way of deterring what it described as "futile" requests.