Published: 13:30, 15 June 2016
Chancellor George Osborne has warned a vote to leave the EU could place a question mark over money the government has allocated to find a solution to Operation Stack.
He also warned of a similar threat to the planned new Thames crossing on a visit to the Hitachi train depot in Ashford.
Both schemes could fall foul of the need to set an emergency budget to cope with a downturn in the economy if there was a Brexit, he said.
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A document published by the campaign group Britain Stronger in Europe detailed how large infrastructure schemes could be at risk because of the need to cut capital spending by £2.4bn.
On plans for a lorry park for Operation Stack, Mr Osborne said: “We have the potential to solve this big issue for residents when the tunnel is blocked.
"We have a proposal that has the support of Kent MPs. We have the money allocated and I want it to go ahead but I can’t honestly say as Chancellor of the Exchequer that I can guarantee it.
"There would have to be an emergency budget and it is projects like Operation Stack that would have a question mark against it.”
On the plans for a new Thames crossing, he said: "These decisions take many many years.
"You have to make sure the funding is there. One of the first thing that happens when there is a recession is you would need to look at big infrastucture projects."
Mr Osborne highlighted the threat to the economy and investment in the south east as the referendum campaign enters its final phase.
"A vote to leave would hurt businesses, hurt investment and cost jobs. There would be difficult decisions - difficult decisions that begin next Friday.
"There would have to be an emergency budget to fill a £30bn black hole.
"Today we are setting out the difficult decisions we would have to take."
He described an exit from the EU as a "lose-lose situation."
"A vote to leave would hurt businesses, hurt investment and cost jobs..." - George Osborne
Leaving the EU would "undo the good we have done", describing it as a "leap in the dark that would hurt our children."
He said a Brexit budget would mean income tax rising by 2p to 22p and health spending would be cut by £2.5bn and education budget cut by £1.2bn.
He was accompanied by former Labour Chancellor Alistair Darling, who described the momentous vote as a "once-in-a-lifetime decision which will decide Britain's position in the world for the next 40 to 50 years."
But he claimed Brexit would lead to a downturn in the economy.
Mr Darling claimed the Leave campaign had a flawed prospectus.
He added: "There would not just be one emergency budget, there would be one
after the other.
"The Chancellor would have to consider cuts to the NHs and schools if we leave."
The pair’s visit comes as polls suggest that the outcome of next week’s referendum is too close to call.
The Chancellor is the latest in a string of political VIPs to head to the county to campaign.
Additional reporting by Adele Couchman