Following a day of confusion over the new visa restrictions imposed by the US president, the Foreign Secretary updated MPs on the consequence for British nationals as he blasted the "divisive and wrong" policy.
Mr Johnson told the House of Commons, following talks held by both himself and Home Secretary Amber Rudd with White House officials, the Government had been assured by the US Embassy "the general principle is that all British passport holders remain welcome to travel to the US".
He added the Government President Trump's executive order will "make no difference to any British passport holder irrespective of their country of birth or whether they hold another passport" from one of the seven Muslim-majority countries affected by the ban.
Mr Johnson admitted there was "understandable concern and uncertainty" by President Trump's actions.
He said: "This is not UK policy, this is not our policy, nor is it a measure this Government would consider.
"I've already made clear our anxiety about measures that discriminate on grounds of nationality that are divisive and wrong."
The Foreign Secretary highlighted to MPs how the "temporary measure" is only intended to last for an initial 90 days.
He added: "This is, of course, a highly controversial policy which has caused unease and I repeat that this is not an approach this Government would take."
Mr Johnson also reminded the House of Commons of the "vital importance of this country's alliance with the US".
He insisted Theresa May's "highly successful" visit to the White House last week had "underlined the strength of that transatlantic alliance".
The Foreign Secretary said: "Where we have differences with the US we will not quail from expressing them, as I have done today.
He added: "But we also repeat our resolve to work alongside the Trump administration in the mutual interests of our countries."
Boris Johnson was grilled by MPs over the impact of Donald Trump's ban
Earlier today, in an apparent contradiction to the UK Government's understanding, the US Embassy had issued an 'Urgent Notice' on its website.
It had told UK citizens who share dual nationality with one of seven mainly-Muslim countries covered by the restrictions not to apply for visas, meaning individuals such as Tory MP Nadhim Zahawi could yet be affected.
But the 'Urgent Notice' was later deleted with the US Embassy not commenting on whether it will be replaced with new advice.
The notice had stated: "Per U.S. Presidential Executive Order signed on January 27, 2017, visa issuance to aliens from the countries of Iraq, Iran, Libya, Somalia, Sudan, Syria and Yemen has been suspended effective immediately until further notification.
"If you are a national, or dual national, of one of these countries, please do not schedule a visa appointment or pay any visa fees at this time.
"If you already have an appointment scheduled, please DO NOT ATTEND your appointment as we will not be able to proceed with your visa interview.
"Please note that certain travel for official governmental purposes, related to official business at or on behalf of designated international organizations, on behalf of the North Atlantic Treaty Organization, or by certain officials is not subject to this suspension."
Donald Trump's Action Plan
Thu, January 19, 2017
What follows is Donald Trump's action plan to 'Make America Great Again' within the first 100 days of Presidency.
1 of 10
FIRST: Propose a Constitutional Amendment to impose term limits on all members of Congress.
We will not be able to proceed with your visa interview.
Last night, the Foreign Office had insisted British dual nationals would not be affected by the ban after Foreign Secretary Boris Johnson won assurances in a phone call with President Trump's son-in-law Jared Kushner yesterday.
A Foreign Office source told Express.co.uk they still believed British nationals were exempt from the visa ban and were working to clarify the US Embassy's new advice, which they expect to be changed.
They said: "The Foreign Secretary’s statement yesterday is based on the clarification he was given by the White House on what the order means for UK nationals.”
It was suggested the contradiction could be due to confusion among American officials over the implementation of President Trump's executive order.
The Foreign Office's official travel advice currently states: "Temporary immigration measures are in place affecting British nationals who hold dual nationality with Libya, Iran, Iraq, Somalia, Sudan, Syria and Yemen."
But in a statement issued last night, the Foreign Office said: "The Foreign Secretary Boris Johnson has today held conversations with the US government and as a result we can clarify that the Presidential executive order only applies to individuals travelling from one of the seven named countries.
"If you are travelling to the US from anywhere other than one of those countries (for instance, the UK) the executive order does not apply to you and you will experience no extra checks regardless of your nationality or your place of birth.
"If you are a UK national who happens to be travelling from one of those countries to the US, then the order does not apply to you – even if you were born in one of those countries.
"If you are a dual citizen of one of those countries travelling to the US from OUTSIDE those countries then the order does not apply to you.
"The only dual nationals who might have extra checks are those coming from one of the 7 countries themselves – for example a UK-Libya dual national coming from Libya to the US.
"The US has reaffirmed its strong commitment to the expeditious processing of all travellers from the United Kingdom."
The notice was later deleted
More than one million Britons have signed a petition calling for President Trump's state visit to the UK to be cancelled following the introduction of his ban.
Mr Johnson is due to make a statement to MPs this afternoon.