Cabinet ministers should “exert their collective authority” and rebel against Theresa May’s proposed Brexit deal, ex-Brexit Secretary David Davis has said.
The PM has suggested a temporary customs arrangement for the whole UK to remain in the customs union while the Irish border issue is resolved.
Brexiteers suspect this could turn into a permanent situation, restricting the freedom to strike trade deals.
“This is one of the most fundamental decisions that government has taken in modern times,” he added.
The article comes ahead of a crucial summit with EU leaders in Brussels on Wednesday which will determine whether or not a deal can be struck.
Mr Davis resigned from his post in July – days after Mrs May’s so-called Chequers deal was agreed by cabinet – saying he did not believe in the plan.
He was soon followed out of government by the then-Foreign Secretary Boris Johnson, who claimed the PM was leading the UK into a “semi-Brexit” with the “status of a colony”.
The pair have been vocal opponents of Mrs May’s direction since returning to the backbenches.
The issue of the border between Northern Ireland and the Republic of Ireland, which will become the UK’s border with the EU, is one of the last remaining obstacles to achieving a divorce deal with Brussels.
Wrangling is continuing over the nature of a “backstop” to keep the border open if a wider UK-EU trade arrangement cannot resolve it.
The EU’s version, which would see just Northern Ireland remain aligned with Brussels’ rules, has been called unacceptable by Mrs May and the DUP.
Mr Davis said the government’s negotiating strategy had “fundamental flaws”, arising from its “unwise decision” to let the EU dictate the principle of the backstop in December, when the two sides agreed a wider settlement on citizens rights and the so-called divorce bill.
Former Tory leader Iain Duncan Smith said it had been a mistake for the prime minister to allow herself to get “boxed in” over the issue of Northern Ireland.
Asked on Sky News’ Sophy Ridge show whether he backed calls for a Cabinet rebellion, Mr Duncan Smith said, “when you no longer agree on a fundamental issue, then it’s probably time that you found yourself on the back benches”.
Davis’s public call to rebellion
By Helen Catt, BBC political correspondent
That David Davis is no fan of Theresa May’s Brexit plan is not surprising.
That he’s choosing to ratchet up the pressure with a public call to rebellion aimed at her most senior ministers is perhaps more so.
The former Brexit secretary’s own resignation from the cabinet in July did not alter the prime minister’s course.
But time to reach a deal with the EU is now considerably shorter, and there have been reports that other senior Conservatives have concerns about the back-up plan for the Irish border too.
The key question is perhaps not so much whom his article might persuade, but whether or not it reflects what some in the cabinet may already be thinking.
Negotiations have continued this weekend between the UK and the EU ahead of Wednesday’s meeting.
On Saturday evening, German newspaper Suddeutsche Zeitung reported a deal had already been reached between Mrs May and the EU, and would be announced on Monday.
But a No 10 source told the BBC the report was “100%, categorically untrue” and negotiations were ongoing.
The paper said it had seen a leaked memo from EU negotiators to EU ambassadors stating: “Deal made.”
Mrs Foster said Mrs May should not back a plan that would “effectively cut Northern Ireland adrift”.
More than three-quarters of NHS trusts, meanwhile, have made no preparations for the UK’s departure from the EU whatsoever – according to documents obtained by the People’s Vote campaign under Freedom of Information requests.
The group also commissioned a YouGov poll of the UK’s doctors and nurses, who – according to the poll – now back another referendum by a margin of three to one.