"You cannot leave part of the United Kingdom in a worse off position."
DUP leader Arlene Foster has accused Boris Johnson of a "betrayal" over Brexit, saying he "broke his word" that a Withdrawal Agreement would not include a customs border in the Irish Sea.
During an interview with
BBC Today, Foster was asked if Johnson's Brexit deal represented a "betrayal" of the DUP.
"I think it says more about the person who broke their word, than me and leadership of the Unionist party," she said.
After the last UK General Election, the DUP propped up the current Conservative government in a confidence and supply arrangement. After Johnson succeeded Theresa May as prime minister, the DUP cheered and hailed Johnson as he entered 10 Downing Street.
However, the relationship between the DUP and the Tory Party has since changed.
"I think Boris wants to get Brexit done - I completely understand that after such a long period of time since the referendum result - but you cannot leave part of the United Kingdom in a worse off position and leave us in a position where we have checks between different parts of the UK," said Foster.
Johnson has repeatedly said that his Brexit deal will not create friction in trading between Northern Ireland and Great Britain, but a recent study by the Treasury found that there would be at some extra paperwork for exporters.
When asked if she can believe the word of Johnson, Foster said: "It says more about Boris Johnson that he moved away from what he said. It's very important for us in Northern Ireland - not just to have the word, but to have the detail.
"We want to see the detail, we did see the detail when we spoke to HRMC officials, and they said that there would be checks between the mainland and Northern Ireland, something that will cause economic instability in Northern Ireland, which will lead to higher costs for retailers and less choice for consumers in Northern Ireland."
When the show's host Justin Webb put things bluntly to Foster by stating that the DUP "played your cards and you lost," Foster replied by saying: "I think it is right for the leadership of unionism in Ireland to try and work with the Prime Minister of the day to try and get the best deal for Northern Ireland - we will always try and do that - we will continue to do that. I think it says more about the person who broke their word than me and the leadership of the Unionist party.
Later in the interview, given Johnson's change of policy, Foster was asked if she's able to take the prime minister on his word.
She replied by saying "once bitten, twice shy" and that the DUP will "certainly be looking for the detail of what this (Brexit agreement) is going to look like".
The DUP leader also said that free-flowing trade between the different nations in the United Kingdom represented an integral part of the union and that Mr Johnson had “moved away” from what he promised her at the Conservative Party conference.
You can listen to the interview in full
here.
