The ex-leader of Theresa May’s Downing Street policy board has said he will not back her Brexit deal if it creates a hard border in Ireland.

George Freeman MP warned that time is running out to resolve the issue which he said is a “red line” for himself and other Conservative backbenchers.

Brexit Secretary David Davis arrived in Brussels on Monday morning where he is expected to try and hammer out an agreement on the rules governing the transition period after the UK leaves the EU.

If an agreement is reached it could be signed off at the end of the week at a summit, though European Council President Donald Tusk is set to make any transition deal conditional on the UK addressing the Irish border issue.

Mid-Norfolk MP Mr Freeman spoke out after a committee report last week branded Ms May’s current plans to allay the need for a border as “blue sky thinking”.

Speaking to BBC Radio 4’s Westminster Hour, he said commitments Ms May had already made as part of her negotiating position are "irreconcilable" with Europe's expectations.

Emphasising that the border issue is a "red line" for him and other Tories, he added: "I would find it very difficult to vote for a Brexit that puts a border back between the north and south in Ireland and creates a cliff edge for investment next spring."

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Ms May has both vowed to leave the EU’s customs union and also maintain no border between Northern Ireland and the Republic.

But EU negotiators have said the two positions are irreconcilable, with the only way to ensure there is no border, being for the UK, or at least Northern Ireland, to stay in full regulatory alignment with Brussels by remaining in the customs union.

Ms May’s current legislative programme has been delayed because Tory rebels are pushing an amendment to the Trade Bill that could force her to stay in the customs union, while Tory whips are unsure they can beat it.

When asked if a forced vote to stay in the customs union could solve the issue, Mr Freeman said accepted that doing so could also anger Brexiteer Tories.

He said: “If colleagues in the House push on the customs union too quickly it'll be seen as a last stand to stop Brexit.

“But if this isn't sorted in six to nine months it'll be very different.”

The biggest issues facing UK on leaving EU Show all 8 1 /8 The biggest issues facing UK on leaving EU The biggest issues facing UK on leaving EU Post-Brexit immigration workers sorting radishes on a production line at a farm in Norfolk. One possible post-Brexit immigration scheme could struggle to channel workers towards less attractive roles - while another may heighten the risk of labour exploitation, a new report warns. PA The biggest issues facing UK on leaving EU Customs union A key point in the negotiations remains Britain's access to, or withdrawal from, the EU customs union. Since the referendum there has been hot debate over the meaning of Brexit: would it entail a full withdrawal from the existing agreement, known as hard Brexit, or the soft version in which we would remain part of a common customs area for most goods, as Turkey does? No 10 has so far insisted that “Brexit means Brexit” and that Britain will be leaving the customs union, but may be inclined to change its position once the potential risks to the UK’s economic outlook become clearer. Alamy The biggest issues facing UK on leaving EU Northern Ireland-Irish border Though progress was made last year, there has still been no solid agreement on whether there should be a hard border between Northern Ireland and the Republic of Ireland. To ensure borderless travel on the island, the countries must be in regulatory alignment and therefore adhere to the same rules as the customs union. In December, the Conservative Party’s coalition partners, the DUP, refused a draft agreement that would place the UK/EU border in the Irish Sea due to its potential to undermine the union. May has promised that would not be the case and has suggested that a “specific solution” would need to be found. Getty The biggest issues facing UK on leaving EU Transition period Despite protests from a small number of Conservative MPs, the Government and the EU are largely in agreement that a transitional period is needed after Brexit. The talks, however, have reached an impasse. Though May has agreed that the UK will continue to contribute to the EU budget until 2021, the PM wants to be able to select which laws made during this time the UK will have to adhere to. Chief negotiator Michel Barnier has said the UK must adopt all of the laws passed during the transition, without any input from British ministers or MEPs. EPA The biggest issues facing UK on leaving EU Rights of EU citizens living the UK The Prime Minister has promised EU citizens already living in the UK the right to live and work here after Brexit, but the rights of those who arrive after Brexit day remains unclear. May insists that those who arrive during the transition period should not be allowed to stay, whereas the EU believe the cut-off point should be later. Getty The biggest issues facing UK on leaving EU Future trade agreement (with the EU) Despite this being a key issue in negotiations, the Government has yet to lay out exactly what it wants from a trade deal with the EU. Infighting within the Cabinet has prevented a solid position from being reached, with some MPs content that "no deal is better than a bad deal" while others rally behind single market access. The EU has already confirmed that access to the single market would be impossible without the UK remaining in the customs union. Getty The biggest issues facing UK on leaving EU Future trade agreements (internationally) The Government has already begun trying to woo foreign leaders into prospective trade agreements, with various high profile state visits to China, India and Canada for May, and the now infamous invitation to US President Donald Trump to visit London. However the UK cannot make trade agreements with another country while it is still a member of the EU, and the potential loss of trade with the world's major powers is a source of anxiety for the PM. The EU has said the UK cannot secure trade deals during the transition period. EPA The biggest issues facing UK on leaving EU Financial services Banks in the UK will be hit hard regardless of the Brexit outcome. The EU has refused to give British banks passporting rights to trade within the EU, dashing hopes of a special City deal. However according to new reports Germany has suggested allowing trade on the condition that the UK continues paying into the EU budget even after the transition period. Getty

Mr Davis is in Brussels to thrash out details of transition arrangements that would come into force when Britain leaves in March 2019, with his EU counterpart Michel Barnier.

The Brexit Secretary has said he can "live with" an implementation period of under two years if it helps to secure an early deal.

The Prime Minister will head to Brussels on Thursday for a meeting of the European Council where she is hoping a deal on the arrangements will be signed off.

Britain had hoped the Council would herald the start of substantive trade talks as well, but Mr Tusk has said they cannot begin until the UK agrees the draft text of the divorce agreement – which is being delayed by a failure to set out how the UK can both ensure there is no border in Ireland and leave the customs union.

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The Common Northern Ireland Select Committee warned last week that Ms May’s pledge of no hard border in Ireland after Brexit can only be achieved if the UK remains fully aligned with EU rules for the foreseeable future.

A report published by the group said there is “no evidence” of the technical solution promised by Ms May, to allow Northern Ireland to break free from the customs union and single market without the return of border posts and checks.

It said the Government’s existing proposals were “blue sky thinking” which would be impossible to implement before Brexit day, now just one year away.