The Business Secretary has sought to calm Tory tensions over Brexit by insisting Britain is "absolutely, unambiguously" leaving the European Union.
Greg Clark intervened after leading Brexiteer Jacob Rees-Mogg warned Theresa May if she delivers "Brexit in name only", with a status quo transition period, the Conservatives will lose the next election.
Mr Rees-Mogg, chairman of the influential European Research Group of backbench Tory Eurosceptics, also told the Prime Minister "the leader is important, the party is more important".
He appeared to put himself on collision course with the Government by warning a "status quo transition", with the UK subject to European Court of Justice (ECJ) rulings, having to accept new laws, and paying into the EU budget, would be "a failure of negotiations" and a "sign of weakness".
But Mr Clark denied that nothing would change during the transition of around two years after exit day in 2019, because Britain would "exercise our sovereign right" to register EU migrants, although they will remain free to live and work in the country.
The Business Secretary's claim came despite the fact that the UK Government's own website acknowledges that EU nationals moving to Belgium, a member state, must register with the authorities within eight days of arriving.
He said a transition period was necessary to allow businesses time to adjust to new rules after Brexit.
Mr Clark told BBC Radio 4's Today programme: "I think it's very important that as we leave the EU, which is absolutely, unambiguously the case that we are, that businesses have been very clear all across the country, large businesses and small businesses as well, that we need to take the time to be able to adjust to the new regime.
"I talk to businesses day in, day out, and they are unanimous in wanting to have that period."
His intervention came after David Davis was forced to play down Cabinet rifts over Brexit and amid rising disquiet among Tory backbenchers over Mrs May's leadership.
The Brexit Secretary on Friday insisted there was "no difference" between himself, Chancellor Philip Hammond and the PM on the outcome they were seeking.
But Mr Hammond's remark on Thursday that the UK's trade relations with the EU would change only "very modestly" after Brexit sparked anger among Tory Eurosceptics and earned him a rebuke from Downing Street.
The Chancellor then risked stoking Tory divisions further by saying the UK should seek a "middle way" in negotiations in order to maximise access to EU markets.
In an apparent attempt to show unity on Friday evening, Mr Davis, Mr Hammond and Mr Clark wrote an open letter to reassure business leaders the UK would maintain continuity with EU rules during transition.
But Mr Rees-Mogg warned the Government against delivering "Brino" - Brexit in name only.
He told the Telegraph: "The less of Brexit you get, the more likely you are to get Jeremy Corbyn.
"If you get a good, clean Brexit and get the advantages from it then the chances of getting Jeremy Corbyn are much diminished.
"If everything is delayed for two years and then there's high alignment, you will find that by 2022 no-one will have noticed any difference from having left.
"Then what will be the point of voting for the party that's implemented it. I'm against 'Brino' (Brexit in name only)."
Mr Rees-Mogg insisted the PM has his "full support" and said Mr Hammond appeared to be "obstructing Brexit".
But he added: "If the Conservative Party doesn't deliver the Brexit that the British people voted for, the Conservatives will not win the next election. The leader is important, but the party is more important.
"Brexit is more important than anyone other than the Queen."
Discontent among Tories has led to reports that the number of MPs who have written to Sir Graham Brady, the chairman of the backbench 1922 Committee, calling for a leadership contest is close to the trigger point needed to force a battle aimed at toppling Mrs May.
Meanwhile, Irish premier Leo Varadkar warned Britain it would have to pay for access to the single market beyond the transition.
"It is the norm that countries that have access to the single market contribute to the budget in some way and Norway does that," he told Today.