THE UK Government will keep spending money on contingency plans for a "no-deal" Brexit until just before the planned withdrawal date of March 29 2019 in case a proposed transition deal falls through, David Davis has said.

Even if political agreement on the transition were reached at this month's European Council summit, the Brexit Secretary told MPs preparations for a no-deal outcome must continue until the plan was formally ratified; probably in the final weeks of this year.

His remarks appear to put him at odds with Philip Hammond, who told the Commons European Scrutiny Committee on Monday he expected to be able to "stand down" preparations for a no-deal Brexit once the transition deal was agreed.

With £700 million already spent on Brexit contingency planning, the Chancellor said he wanted to "make sure that we are not spending money on outcomes that have been effectively ruled out at any stage".

Crashing out without a deal in March 2019 would probably require significant investment, whether on additional customs officials or lorry parks at ports.

A transition deal would ease the pressure by giving businesses and authorities about two years to prepare for an orderly departure.

Any transition arrangement agreed at the March 22/23 summit would first have to be put into its final legal form before being sent in October to the UK and European parliaments for ratification.

But Mr Davis told the Commons committee that the Government could not take for granted that a deal reached with the other 27 EU member-states in Brussels would come into effect as planned.

It would not be possible, he explained, to "stand down" contingency preparations "until we have got to the point of agreement later in the year."

The Secretary of State stressed: "It's highly improbable, but always possible, that the deal will come apart at the end for some wholly unpredictable reason. A responsible Government has to be ready for that outcome, just as a matter of good practice."

Mr Davis played down the difficulties which post-Brexit customs arrangements might cause to companies like Airbus, which operates a "just-in-time" delivery system for parts moving between bases in the UK and continental Europe.

Earlier this week, Katherine Bennett, senior vice-president of Airbus UK, said the company - one of Britain's largest manufacturing employers - would decide very soon about stockpiling parts and might have to "think differently" about its operations if conditions were not right.

But Mr Davis said he had spoken to Airbus's chief executive and assured the committee: "Moving wings from the North-West and moving other components backwards and forwards, I don't foresee that they would have a major problem there."

Labour’s Darren Jones, whose Bristol West constituency adjoins Airbus's Filton plant, told the Secretary of State: "With respect, they wouldn't have said they have a problem if they didn't have a problem...They are still not happy and I suggest you have further conversations."

Mr Davis also played down differences with the European Commission over arrangements for the Irish border, insisting issues raised by Brussels were "largely resolvable" as part of a "pragmatic" agreement allowing tariff-free trade and mutual recognition of standards.

By publishing its fall-back option of harmonising customs rules between Northern Ireland and the Republic before discussing the UK's proposals in depth, Brussels was "putting the cart before the horse", said the Brexit Secretary, adding: "We've done quite a lot of building the cart."