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A Whitehall “logjam” caused by the EU referendum in June could force yet another delay to the government’s decision on a new runway for Heathrow or Gatwick.

Insiders quoted by the London Evening Standard claim it is among a raft of major decisions competing for time in a one-month window between the referendum and the summer parliamentary recess.

September is increasingly seen as the earliest date for a new southeast runway site to be chosen, but a longer wait is not being ruled out.

Prime minister David Cameron originally pledged a decision by last December after the Aviation Commission last summer backed expansion of Heathrow.

No 10 officials strongly denied claims made by MPs and ministers that the government is “paralysed” by its battle to win the referendum on June 23.

But one senior Tory said: “The Prime Minister is absolutely consumed by the referendum and a lot of decisions are piling up in the in-tray.”

An industry figure who deals with government said: “We’re seeing every Whitehall department fighting to get its decisions timetabled to be taken in July.”

A Department for Transport spokesman said: “We have accepted the case for airport expansion in the southeast and we are further considering the environmental impacts.

“We will take account of any relevant evidence and expect to conclude this work by the summer.”

A government report last week showing that diesel cars being sold in the UK emit an average of six times more nitrogen oxide in real-world driving than the legal limit used in official tests prompted a call by the boss of Gatwick for the government must redraft its air quality plan.

Gatwick chief executive Stewart Wingate claimed the findings were a “hammer blow” for Heathrow expansion.

“It also obviously means the Government will have to revisit its air quality plan,” he said.

Heathrow rejected the claim about its plans for a third runway, which it says can operate within EU air quality rules.

It said: “Heathrow’s forecasts are modelled on real-world emissions data.”

The Department for Environment, Food and Rural Affairs said: “We will consider any revisions and, if necessary, update our air quality plans.”