Boris Johnson has branded suggestions he is set to quit as Foreign Secretary over Brexit as "lies" after Cabinet tensions on EU withdrawal broke into the open.
Mr Johnson attacked Liberal Democrat leader Sir Vince Cable after he referred to rumours the Foreign Secretary may resign as a Cabinet rift emerged over whether a three-year post-Brexit transitional scheme for migrants would come into force.
A spokesman for Mr Johnson said: "Vince Cable is making this stuff up and maybe he should take more time to think up some policies rather than wasting his time on peddling lies."
The spat erupted after the Lib Dem leader seized on public differences between International Trade Secretary Liam Fox and Chancellor Philip Hammond over the transition plan as he said the Cabinet had descended into "civil war".
Tory Brexit tensions heightened as Dr Fox insisted unregulated free movement of labour after Brexit would "not keep faith" with the EU referendum result and that the Cabinet had not agreed a stance on immigration.
This appeared at odds with Mr Hammond's signal that free movement would continue for a three-year period in all but name, with an added element of migrants having to register in the UK.
Mr Johnson has yet to comment publicly on Mr Hammond's transition plans.
Dr Fox said he had not been involved in any discussions on migrant transitional arrangements.
Former Brexit minister David Jones said Dr Fox and Mr Johnson, both out of the country when Mr Hammond announced the transition plans, were "clearly being kept out of the loop".
Responding to Mr Johnson, Sir Vince told the Press Association: "Does he support the position of Philip Hammond or Liam Fox? Because he can't support both.
"And if Philip Hammond secures a three-year transitional deal, can Boris Johnson confirm he will stay in the Government and support the policy?"
The clash came after Mr Hammond used an interview with Le Monde to down play claims Britain could try to become a Singapore-style low tax economy if it does not get the Brexit deal it wants.
He said: "I often hear it said that the UK is considering participating in unfair competition in regulation and tax.
"That is neither our plan nor our vision for the future. The amount of tax we raise as a percentage of our GDP puts us right in the middle of the pack.
"We don't want that to change, even after we've left the EU.
"I would expect us to remain a country with a social, economic and cultural model that is recognisably European."
Labour's shadow foreign secretary Emily Thornberry told BBC Radio Four's Westminster Hour: "In the last year the Government has done nothing, I mean, seriously, done nothing apart from try and argue amongst themselves, position amongst themselves, as to what the right approach will be."
Health Secretary Jeremy Hunt said he "didn't recognise this picture" of Cabinet splits over Brexit.
He told BBC Radio 4's Today programme there was unity in the Cabinet on delivering a Brexit that restores control over Britain's laws, borders and money.
Mr Hunt said: "If you look at where we are now compared to where we were a few months ago, we've sent some very positive messages to Brussels about what we want.
"The other thing that we are completely united on as a Cabinet is that we want Brexit to make Britain more global, and not more insular.
"That means that it has to be a Brexit that works for business, it has to work for the NHS, the NHS needs to recruit doctors and nurses from all over Europe and that is going to continue after we leave the European Union."
Mr Hunt added there would be no cliff-edge after Brexit and there would be an implementation period of no more than three years after the UK's exit in March 2019.