In a coordinated push to save plans for a customs relationship that is “as frictionless as possible” after Brexit, businesses and Tory backbenchers - including one of the ringleaders of an attempted coup against the Prime Minister last year - spoke up to defend the government’s plans from Brexiteers led by Jacob Rees-Mogg.
Mrs May was forced to ask officials for revised proposals on post-Brexit customs after she failed to get support from her ‘war cabinet’ for a complex arrangement that would see the UK collect duties on goods in transit to the EU in order to keep trade flowing freely and maintain an open border in Ireland.
The addition of Sajid Javid, the new Home Secretary who replaced Amber Rudd last week, to the cabinet subcommittee on Brexit upset the balance in the key group of ministers and gave eurosceptics the advantage.
In a bid to calm fears among her cabinet and Mr Rees-Mogg’s European Reform Group of Tory backbenchers, Ms May said she had an "absolute determination to make a success of Brexit, by leaving the single market and customs union” in an article for the Sun on Sunday.
But the government also went on the offensive, sending the Business Secretary Greg Clark onto the BBC’s Andrew Marr show to argue that without a customs partnership, thousands of jobs will be at risk.
Mr Clark’s message was endorsed by Ms Rudd, who posted on twitter to say the government was planning “for a Brexit that protects existing jobs and future investment".
Pro-EU former ministers Nicky Morgan, Anna Soubry and Justine Greening also toured radio and TV stations to shore up the Prime Minister’s stance, with Ms Morgan hitting out at “sabre-rattling and leadership threats" by Brexiteers.
Mrs May even got a boost from the former Tory chairman Grant Shapps, who led calls for her to be ousted following last year’s election setback but yesterday said the Prime Minister could lead the Tories into the next general election.
The British Chambers of Commerce and Confederation of British Industry also called on the government to stand by its current plans, saying it was important to maintain the status quo on frictionless trade until a new arrangement is in place.
Mr Clark opened the door to extending a transition period on customs with the EU, saying post-Brexit customs arrangements would be implemented "as soon as you can do" and admitting that technology and infrastructure needed for border checks may not be in place until 2023.
Mr Clark cited the example of Toyota, which employs 3,500 people in the UK, warning were fears over how the firm's "just in time" manufacturing model would operate with customs checks.
But Mr Rees-Mogg dismissed those concerns, telling ITV's Peston On Sunday: "This Project Fear has been so thoroughly discredited that you would have thought it would have come to an end by now.
"We trade successfully all over the world. The delays on goods coming into Southampton are tiny.
"We will have control of goods coming into this country - we will set our own laws, our own policies, our own regulations, and therefore we will determine how efficient the border is coming into us."
He claimed a customs partnership would effectively keep the UK in the EU, and said it would be "odd" for the Prime Minister to back a policy that breached her commitment on leaving both the customs union and single market.