The Democratic Unionist Party is prepared to vote against the budget if their red lines for an EU deal are ignored next week, Sky News understands.

The 10 Unionist MPs prop up Theresa May's government, which has no majority, as part of a confidence and supply deal in which they are relied on to vote through the government's budgets.

Party leader Arlene Foster has made clear that any Brexit deal in which Northern Ireland is treated separately to the rest of the UK, or faces extra checks along the border with Ireland, would be unacceptable to her party and that this is a "blood red line".

The threat to vote down the budget, revealed by Sky sources, will pile pressure on the Cabinet to deliver a deal in which the whole United Kingdom remains in a temporary customs union with the EU until a solution is found which would avoid regulatory or customs checks on the border.

But such an arrangement would provoke outrage from Conservative backbenchers, who say Britain would find it very difficult to end such an arrangement as it would leave our exit date in the hands of the EU.


Steve Baker, Conservative MP for Wycombe, said he believed "at least 40" of his colleagues would vote against a deal along the lines the prime minister has proposed which would include this "backstop" for Northern Ireland.

Tory Brexiteers this week denied reports that they would vote down the Budget if the prime minister fails to change course, and there is cautious optimism in the cabinet that they can convince enough MPs to vote for a deal she strikes in Brussels.

A DUP source told Sky News: "It is unacceptable that we would be treated differently to the rest of the UK.

"We will not be bounced into anything.

"If Theresa May doesn't take our concerns on board, she may not be the leader to take us through Brexit."