Northern Ireland's former first minister Arlene Foster has claimed British Prime Minister Boris Johnson gave into pressure to accept the Northern Ireland Protocol "as proposed" by the Irish Government.
Mrs Foster also criticised Tánaiste Leo Varadkar and Minister for Foreign Affiars Simon Coveney for their handling of the Brexit process, blaming their "aggressive nationalism" on the growth of Sinn Féin.
The UK and EU have brought forward proposals in a bid to resolve the dispute over the protocol.
The mechanism is part of the Brexit divorce deal negotiated by the UK Government and signed by Mr Johnson aimed at avoiding a hard border on the island of Ireland.
The terms effectively kept Northern Ireland in the single market, creating a border down the Irish Sea.
Mrs Foster said she believes the protocol played a big role in her ousting as DUP leader earlier this year.
"We stood against this type of arrangement and were successful at resisting this type of outcome so long as we held the balance of power at Westminster," Mrs Foster told the Sunday Times newspaper.
"But, unfortunately, the moment the prime minister had a majority he made a decision to get Brexit done and deal with the fallout later.
"Of course it is hugely disappointing that Boris, under pressure, gave into the protocol as proposed by Leo Varadkar, and all that it has brought.
"When it came into being in January (2020), I and colleagues tried to deal with the problems as they arose but it soon became clear this wasn't possible and fundamental change was needed.
"There is no doubt the implementation of the protocol was hugely damaging to my time as leader.
"I couldn't have done any more to alert the Prime Minister to the problems that would arise, but when you are the DUP leader you are blamed regardless."
Mrs Foster also said the relationship with the Irish Government has never "been at such a low ebb", particularly with Mr Coveney and Mr Varadkar.
"They refuse to deal with the practical reality of the principle of consent, ie. that Northern Ireland is a full member of the UK," Mrs Foster added.
"They have used their position to undermine the constitutional position here.
"I can only put their aggressive nationalism down to the growth of Sinn Féin."