THE government’s plan to keep the Irish border wide open after Brexit would leave a back door into Britain for illegal EU immigrants, it has emerged.

A detailed proposal on how to solve the Ireland dilemma also unveiled yesterday also revealed a pledge to keep the 65 year-old principle of free movement between the UK and Ireland.

4 Theresa May’s Brexit plan to keep our border with Ireland wide open would leave a back door into Britain Credit: PA

The two pledges are key to upholding Ulster’s peace process, Theresa May said.

The Brexit ministry’s paper also dropped a strong hint for the first time that EU citizens will still be able to come to Britain for tourism without the need for a visa after Britain’s EU exit.

But officials conceded that means all EU citizens will be able to travel to Ireland and then on into the UK via Northern Ireland unchecked.

Immigration bosses would be forced to rely on detecting illegals only once they have arrived in Britain instead of stopping them at borders.

One senior official said: “From an immigration control perspective, immigration control has never been about the physical blocking of people at the physical border.”

“Access to the UK labour market implies its own set of checks.”

4 PM’s proposal concedes all EU citizens will remain free to travel to the Republic - and then on into the UK via Northern Ireland unchecked Credit: AFP

Brexit will mean a massive reduction in pull factors for migrants coming to the UK anyway if they are not allowed to work, the Brexit ministry argued.

Issuing the pledges yesterday, the PM said: “No one would pretend our history has always been smooth.

“But as the UK begins a new chapter, it will not mean turning our back on the historic progress that has been made within Northern Ireland”.

It also emerged that the UK is ready to stump up extra cash to contribute to continuing EU funding to bolster the peace process.

Irish senator Mark Daly, the Deputy Leader of Fianna Fáil, warned the open border arrangement would create “a smugglers’ charter” for people as well as contraband goods.

But Ireland’s foreign minister welcomed the government’s commitment to the open border as “a significant step forward”.

Simon Coveney also said it met much of Dublin’s demands for an exit deal, but warned there are “still significant questions” on how to operate the invisible border and agreeing it will be “difficult” during negotiations.

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Lib Dem home affairs spokesman Ed Davey branded the government’s plan as having “more holes in it than a colander”.

Mr Davey added: “The Brexiteers claimed it was worth damaging the UK economy to reclaim control of our borders, now we’re told even this isn’t going to happen".

4 At a briefing this morning an official said 'there is not a totally harmonised UK-Ireland immigration system for non-EEA nationals' Credit: Reuters

4 Brexit Secretary David Davis said 'the UK and Ireland have been clear all along that we need to prioritise protecting the Belfast Agreement in these negotiations' Credit: PA

Earlier it emerged that talks on a new trade deal with the EU may be delayed until December.

They were due to start in October after EU leaders declared there had been “sufficient progress” made on Britian’s exit terms.

But stand offs over the divorce bill and waiting for a more pro-British German government to arrive may push back the tight timetable by two months.