- Video report by ITV News Political Editor Robert Peston
Theresa May has told ITV News of her frustration towards Boris Johnson after he urged her to tear up her Brexit Irish "backstop" agreement with the EU.
The Prime Minister specifically highlighted Mr Johnson's argument that discussions on the issue of a Northern Ireland backstop should only take place once the UK has left the European Union.
Mrs May told ITV News Political Editor Robert Peston that what she found "frustrating" about Mr Johnson's proposals was that "he appeared to be saying that he wanted to tear up something that is effectively a guarantee for the people of Northern Ireland.
"I believe, as a unionist, that it is important that we recognise the needs and concerns of people in Northern Ireland, as they're the one part of the UK that has a land border with a country in the EU," the Prime Minister said.
While Mrs May said that Mr Johnson had been a "good foreign secretary", she maintained his Brexit proposals were wrong.
- Watch the interview in full
Mrs May continued that a backstop was designed "never to be used" and would "only be necessary in limited circumstances", such as if there was a time lag after March 29, 2019, on putting new arrangements into place, to help ensure frictionless trade and no hard border between Northern Ireland and Ireland.
The DUP - who are propping up the Conservative Government - has said it will not support a plan which could lead to any new checks on goods coming into Northern Ireland from elsewhere in the UK, as it would lead to a border in the Irish Sea which would "separate" them from the rest of the UK.
Both sides have agreed the need for a backstop but not how it should operate.
Mrs May said the Government was currently working on a new offer on the issue of the Irish border to put to the European Commission as she currently "could not accept what the EU has put forward".
She continued that the EU should give the UK more detail on what its issues with the Irish border proposals in the Chequers plan were, "and if they have counter-proposals, let us know what those counter-proposals are".
Mrs May also said she remained "committed" to reducing immigration to tens of thousands, as set out in her General Election manifesto.
Earlier on Tuesday, Mrs May announced that high-skilled workers will be given priority over those who head to the UK for low-paid jobs under new immigration rules post-Brexit.
The Prime Minister said visas to migrants would be decided on "the contribution they can make to our economy" and "the skills that we need".
"Once we leave the EU we'll be ending free movement once and for all, and that's what our proposal does," Mrs May said.
The Prime Minister confirmed that EU countries will be treated the same as those across the rest of the world when the new system is introduced after the Cabinet agreed the move last month.
Mrs May conceded that it would "take time" to bring immigration down to the tens of thousands as rules would "constantly" need to be looked at, but "having the ability to bring control to people coming from the EU will help in that process".
In a wide-ranging interview, Robert Peston also asked the Prime Minister what she would like her legacy to be.
The 62-year-old said she wanted housing to be her legacy and ensure that "more homes are being built in this country, because I really worry about a situation where many young people feel they're never going to own their own home... because it's a part of the aspiration that each generation has and ensuring each generation is better off than the last generation".
The Prime Minister said she also wanted to ensure that the UK has "the economy of the future" and that British workers are trained and skilled to be able to "take on the well-paid jobs of the future".
Robert Peston also questioned the Prime Minister on whether she had any regrets on her time in office, focusing on the fact that when she took power, Mrs May stated that capitalism - a key tenet of Conservative policy - was not working for many people in the UK.
The Maidenhead MP insisted she had "recognised the concerns of people in this country", such as the fear that they were being left behind by globalisation, but it was important to note the successes of capitalism.
"In recognising those concerns and addressing those concerns it's important that we also recognise that it's free markets, it's capitalism, it's open economies, it's trade around the world, that have brought many of the great developments in human life," Mrs May said.