International Trade Secretary Liam Fox has launched an extraordinary attempted power-grab on Boris Johnson's Foreign Office over who should control Britain's foreign commerce policy, a leaked letter reveals.
Just weeks after the two Brexit campaigners were elevated to the Cabinet by Theresa May, Dr Fox told the Foreign Secretary that his newly-created International Trade Department should be handed control of economic diplomacy.
The Sunday Telegraph, which obtained the letter, said the Prime Minister was copied in to the correspondence and was unimpressed, while Mr Johnson rejected Dr Fox's demands.
The International Trade Secretary insisted it would be "rational" to transfer the responsibilities to his department as he criticised the separation of duties within government.
In a sign of tensions boiling over as ministers wrestle with the enormously complex task of delivering Brexit, Dr Fox wrote: "In my first few weeks as Secretary of State for International Trade it has become clear to me that existing cross-Whitehall structures have meant that HM Government has not taken the holistic approach it might have on trade and investment agendas.
"For British trade to flourish there are clear requirements on us: to build the trade framework in markets through trade policy, to establish the conditions for trade and investment through foreign diplomacy, and to reap the harvest of those efforts.
"The role played by economic diplomacy is crucial to delivery of the objectives I have been set by the Prime Minister as International Trade Secretary and I believe it is imperative that this capacity is fully aligned with Government resources delivering trade and investment for the UK.
"If we are to have a rational restructuring I think there is a reasonable proposition to transfer the economic diplomacy function from the Foreign and Commonwealth Office into the Department for International Trade."
The pair were appointed alongside Brexit Secretary David Davis as part of a trio of Cabinet ministers who campaigned for Britain to leave the European Union and who are now tasked with delivering it.
Mr Johnson's appointment as Foreign Secretary came as a major surprise and the creation of two new posts for Dr Fox and Mr Davis sparked speculation over what his role may be.
Mr Davis last month acknowledged that ''even within government there'll be tensions'' over the exit strategy as he and Mrs May appeared to disagree over the timetable for triggering Article 50 to begin the formal process of leaving the EU.
A government spokesman said: "We don't comment on leaked documents.
"Alongside other departments, the FCO (Foreign Office) are seconding a small number of staff with relevant expertise to the new Department for International Trade.
"This is all part of the cross-government effort to ensure we make a success of Brexit."