THE Army might have to guard Britain's borders if the country crashes out of the EU without a deal, MPs have been warned, as Amber Rudd undermined the UK Government's Brexit strategy by saying a no-deal scenario was "unthinkable".

Appearing before the Commons Home Affairs Committee alongside the Home Secretary, Philip Rutnam, the department’s top civil servant, told MPs that it would be unwise to rule out using troops to police the borders in a no-deal Brexit. However, he stressed that the use of the Army would be an “absolute last resort”.

Ms Rudd revealed how 1,200 extra staff were being recruited to provide an “easy access” registration process for some three million EU nationals, which would begin by the end of 2018. She stressed how the “default position” of the Government would be to accept applications.

However, as the row over a no-deal scenario intensified the Secretary of State underscored the rift at the top of government and expressed a view that not only contradicted Theresa May’s strategy but appeared to undermine it.

In a Commons statement, David Davis made clear that retaining the possibility of a no deal was central to the Government’s approach to the Brexit talks.

Stressing how ministers were "straining every sinew" to secure a comprehensive deal covering the future relationship with the European Union after Brexit in March 2019, the Brexit Secretary told MPs how it was vital that in a negotiation you "have to have the right to walk away; if you don't, you get a terrible deal".

He accused EU negotiators of “using time pressure to see if they can get more money out of us and, bluntly, that's what's going on."

The Secretary of State added: “The maintenance of the option of no deal is both for negotiating reasons and sensible security. Any Government doing its job properly will do that.”

But Ms Rudd, who was a prominent campaigner for Remain during the EU referendum, was asked about the possibility that the UK could walk away with no deal "of any form, and replied: “I think it is unthinkable that there would be no deal.

"It is so much in their interest as well as in ours; in their communities', in their families', in their tourists' interests to have something in place. We will make sure there is something between them and us to maintain our security," insisted the Home Secretary.

Downing Street attempted to play down the difference between Ms Rudd and her Cabinet colleague.

A No 10 spokeswoman said: "If you look at her words in full, she's referring to the fact that a deal is in the best interests of both sides and that's something the Prime Minister absolutely agrees with."

But Labour’s Chukka Umunna, on behalf of Open Britain, which campaigns for closer ties with the EU, said the differing views showed the Government was “in total chaos over their threat to leave the EU with no deal”.

The London MP said Cabinet division was increasing the likelihood of Britain crashing out of the EU with an “extreme, destructive Brexit that would put jobs at risk”.

Meanwhile, Ireland’s Taoiseach Leo Varadkar said European leaders were finding it hard to understand the UK's position on Brexit due to mixed messages from the Government.

"It's still not clear what the UK actually wants in terms of a new relationship because, on the one hand, it seems the UK wants to have a close trading relationship with Europe like it has now but it also seems to want something different and it is very hard for us as European prime ministers to understand exactly what the UK wants the new relationship to look like," he said.

Ahead of this week’s EU summit, which begins on Thursday when the Prime Minister will raise Brexit over dinner, Mrs May continued with her diplomatic push, speaking on the phone to Italian counterpart Paolo Gentiloni.

However, it seems almost certain the EU27 will reject the UK’s push to get trade talks underway, insisting there has not been sufficient progress on resolving the divorce bill.