The leader of the Vote Leave campaign has warned the Bank of England governor he will be “very foolish” if he tries to delay Brexit.

Matthew Elliott turned on Mark Carney after the governor was reported to be working on a 'secret plan’ for a transitional arrangement to keep Britain in the single market until 2021.

He said any attempt to slam the brakes on Britain’s EU exit would “go down very badly” with the majority who voted for it, as it was revealed that Theresa May faces a second legal challenge.

Mr Elliott also criticised the Prime Minister for not asking Parliament to vote through the Article 50 withdrawal notice last summer, when there was a “bounce” from the referendum result.

He insisted it was “for the birds” to argue the referendum result was anything other a vote to leave both the single market and the EU’s customs union.

And he said the Leave side “believed sincerely” that an extra £350m would be handed to the NHS when Britain leaves - although the government now faces a huge Budget black hole through to at least 2021.

Speaking at an event entitled ‘What does Leave mean?’, Mr Elliott said: “If the governor is going to try to delay Brexit in any way he would be very foolish and would be going against the will of the people.”

Mr Carney has held private meetings with business leaders on a plan for the current trading rules – almost certainly including freedom of movement for EU citizens – to stay until 2021, the Sunday Times said.

But Mr Elliott insisted both sides in the Brexit fight had understood a Leave vote meant leaving the single market – despite claims a Vote Leave leaflet said exactly the opposite.

He said: “The idea that we are going down some sort of Norwegian-style option is, I think, for the birds.”

On the triggering of Article 50 – a controversy heading to the Supreme Court next week – Mr Elliott said: “It might have been better to have put that Bill through back in September, shortly after the referendum.”

During the central London event, Mr Elliott, who was Vote Leave’s chief executive, faced some anger from younger people who accused him of spreading “lies” about the NHS and immigration.

But he insisted many students had swung behind Brexit when Vote Leave argued it fitted with their “internationalist, global outlook”, by offering the prospects of fairer migration and new trade deals.

Setting out the “12 days of Brexit” – the key events that led to Leave’s triumph - Mr Elliott picked on David Cameron’s failure to strike a meaningful renegotiation of Britain’s EU membership, back in February, as the most important.

He noted how the deal – curbing EU migrants ability to claim benefits, but offering no cut in overall numbers – had prompted headlines reading ‘Is That It?’ and comparisons with Neville Chamberlain.