The PM played down the Bill amending the protocol – being presented to Parliament this afternoon – suggesting the changes were ‘relatively trivial’.
They are expected to include unilaterally creating a check-free ‘green channel’ for goods bound for Northern Ireland from mainland Britain.
He insisted it would be an ‘overreaction’ for Brussels to follow through on threats of trade reprisals.
But Labour has accused the Government of ‘law-breaking’ and there have also been signs of resistance within Tory ranks, with some MPs circulating a note warning the plan will be highly damaging to the party’s reputation.
Meanwhile, Northern Ireland Secretary Brandon Lewis has made clear to the DUP that the legislation will not be activated unless it agrees to get powersharing back up and running.
Mr Johnson told LBC: ‘It’s the right way forward. What we have to respect – this is the crucial thing – is the balance and the symmetry of the Belfast/Good Friday Agreement.
‘We have to understand there are two traditions in Northern Ireland, broadly two ways of looking at the border issues. One community at the moment feels very, very estranged from the way things are operating and very alienated.
‘We have just got to fix that. It is relatively simple to do it, it’s a bureaucratic change that needs to be made.
‘Frankly, it’s a relatively trivial set of adjustments in the grand scheme of things.’
Mr Johnson disagreed with claims that the move breaks international law, arguing that ‘our higher and prior legal commitment as a country is the Belfast/Good Friday Agreement and to the balance and stability of that agreement’.
Foreign Secretary Liz Truss (left) is publishing the Bill today despite threats from the EU’s Maros Sefcovic (right)
There have been warnings that the protocol is disrupting the careful peace balance in NI
The PM (pictured on a visit to Cornwall today) played down the Bill amending the protocol – being presented to Parliament this afternoon – suggesting the changes were ‘relatively trivial’
Mr Johnson said a trade war would be a ‘gross overreaction’ by Brussels.
‘All we are trying to do is simplify things, actually, to remove the barriers to trade between Great Britain and Northern Ireland,’ he said.
It would be ‘preposterous’ to respond with trade restrictions ‘when all we are trying to do is have some bureaucratic simplifications between Great Britain and Northern Ireland’.
In a call this morning, Irish foreign minister Simon Coveney warned Liz Truss that introducing a Bill to unilaterally amend the Northern Ireland Protocol will breach international law and ‘deeply damage’ relationships.
Ms Truss also held a call with the bloc’s vice-president Maros Sefcovic, saying afterwards: ‘Our preference is a negotiated solution, but EU must be willing to change the Protocol itself.’
The legislation will give ministers powers to override elements of the protocol, which was jointly agreed by the UK and EU as part of the Brexit Withdrawal Agreement to keep the Irish land border free-flowing.
The arrangements instead require regulatory checks and customs declarations on goods moving between Great Britain and Northern Ireland.
Unionists in Northern Ireland have condemned the international treaty, claiming it has undermined the region’s place within the United Kingdom.
The DUP has blocked the formation of a new power-sharing government at Stormont following last month’s Assembly election in protest.
The Bill due to come before Parliament will see the Government move without the consent of the EU to change the terms of the protocol in a bid to reduce the checks on the movement of goods across the Irish Sea.
This could include allowing ministers to remove all customs processes for goods moving within the United Kingdom and enable the frictionless movement of agri-food goods staying within the UK.
It could also see businesses in Northern Ireland given the ability to choose whether to follow UK or EU regulations, depending on who they are trading with.
The EU has made clear that such steps would represent a breach of international law and could prompt retaliatory action from the bloc.
The Financial Times reported that an internal note had been circulating among Tory MPs opposed to the Bill, saying: ‘Breaking international law to rip up the Prime Minister’s own treaty is damaging to everything the UK and Conservatives stand for.’
Mr Lewis has said he hopes the Bill will persuade the DUP to support the re-establishment of the Stormont institutions.
He has also said the Government will set out its legal position on the Bill when the legislation is introduced to Parliament on Monday.
Mr Lewis told Sky News on Sunday: ‘What we’re going to do is lawful and it is correct.
‘We will be setting out our legal position on this. People will see that what we’re proposing resolves the key issues within the protocol that don’t work.’
But shadow chancellor Rachel Reeves said ‘it does look like the Government plans to break international law’.
She said: ‘This Government seems to be developing a record for law-breaking and it is not one that the Labour Party can support.’
While Mr Lewis committed to publishing the Government’s ‘legal position’ on the matter, he insisted ‘governments don’t publish details behind advice given to ministers’.
Downing Street has said it will share only ‘a summary’ of the legal advice it received with the public, which has led to accusations of a ‘cover-up’.
Liz Truss held a call with the EU vice-president Maros Sefcovic this morning
A No 10 spokesman said on Friday: ‘The Bill has been agreed by the relevant cabinet committees and will be introduced to Parliament on Monday.
‘We will, alongside the Bill, publish a summary of the legal advice.’
Labour’s shadow Northern Ireland secretary Peter Kyle said it is ‘incumbent on ministers’ to release the maximum possible legal advice, with ‘transparency about its origins’.
Liberal Democrat Northern Ireland spokesman Alistair Carmichael said the public deserves ‘full transparency’ over the plan’s legal basis, warning he suspects a ‘cover-up’.
Asked why Downing Street was publishing only a summary of the legal advice, and not disclosing it in full, Mr Lewis told Times Radio: ‘Well, governments don’t publish details behind advice given to ministers, that’s part of … we have to have that free and open discussion as they’re formulating policy.
‘But we are going to set out the Government’s legal position and our methodology for that.’