The costs of preparing Kent’s motorways to hold thousands of lorries in the event of disruption caused by a no-deal Brexit has rocketed to £35m - partly due to a controversial plan to use the M26 to hold HGVs.

MPs have queried the rising costs, which includes plans for the M20 between Ashford and Maidstone to be a holding area for hauliers. That was originally expected to be about £20m. In the event of disruption, there would be a contra-flow on the London-bound motorway to help keep traffic moving.

The latest forecast for spending on what is known as Operation Brock reveals that part of the increase is attributable to recently-revealed plans to also use the M26 as an additional lorry holding area.

In a report by the all-party public accounts select committee, MPs state: “The Department told us the project is now expected to cost £35m in 2018-19, £30m on the M20 and £5m on the M26. The cost is being met out of Highways England’s budget.”

Worryingly, the report says: “The DfT told us it was becoming less confident that the overall programme was on track. There was still uncertainty about the likely outcome of the negotiations and the timetable of events. The later that decisions are taken, the harder it will be to have contingency plans in place.”

A DFT spokesperson said: “We disagree with the committee’s conclusions which are not accurate and we are both disappointed and surprised that they have failed to reflect the evidence set out in the NAO’s report, which found that the department has made a determined effort in its preparations and achieved a great deal.”

Meanwhile, the transport minister Jesse Norman, has been warned by Kent MPs that using the Manston airport site as an emergency lorry park as part of Operation Brock is fraught with problems.

At a meeting, held on Tuesday, Dover MP Charlie Elphicke and North Thanet MP Sir Roger Gale, along with Port of Dover chairman Richard Everitt, flagged up long-standing concerns over using Manston. The key concern remains how HGVs will leave the site once the motorway is cleared.

Mr Elphicke said: “If the EU seeks to cause queues at Dover and Calais in the event of no deal we need to make sure our local roads are kept clear. People need to be able to get to work and carry on as normal.”

“The minister was left in no doubt of the serious concerns many of us have about using Manston Airport as a lorry park.”