Fianna Fáil leader Micheál Martin has launched a strong attack on Fine Gael during his speech at the party's annual Wolfe Tone commemoration.
Speaking in Bodenstown, Kildare, Mr Martin said that his party had succeeded in stopping many of the most damaging Fine Gael policies by blocking what he called their increasingly right-wing agenda and focus on tax cuts for the wealthiest.
He said the Government was drifting and was failing to tackle problems with urgency or ambition.
Mr Martin referred to Minister for Social Protection Leo Varadkar as a "PR-obsessed minister".
On Brexit, Mr Martin said the actions of the British government had been nothing short of shambolic and its ministers had been cavalier and grossly unprofessional.
He said Ireland was facing a deep and rising threat and the decision would affect the country permanently and Ireland must diversify its markets and reduce its reliance on trade with Britain.
Mr Varadkar has strongly hit back at Mr Martin's criticism saying the speech was akin to something Donald Trump would deliver.
Mr Varadkar accused Mr Martin of mis-characterising Fine Gael and taking cheap shots at other politicians.
He said the Fianna Fáil leader should have used his Bodenstown speech to offer a vision of the future worthy of Wolfe Tone rather than invective more typical of Mr Trump.
Government Chief Whip Regina Doherty said she was "disappointed, but not surprised", to hear Mr Martin say Fianna Fáil had succeeded in blocking Fine Gael’s "increasingly right-wing agenda".
She said it was "simply not true and just the latest example of Deputy Martin’s attempt to re-write history and twist reality".
She added: "Fine Gael will not apologise for seeking to reduce taxes to give workers a break and make our economy more competitive. However, as a party, we also prioritise targeted investment in key public services. Budget 2017 is a firm example of that."
Sinn Féin president Gerry Adams earlier said: "I want to welcome some of Micheál Martin's remarks on the implications and challenges of Brexit today, however it's one thing to lambaste the British government, even though that's justifiable, the main focus has to be on what the Irish Government is doing, or what it's not doing.
"The Taoiseach has yet to clarify claims made by the British Secretary of State that measures have been agreed to put immigration controls at Irish ports and airports. That is totally unacceptable
"The Government's focus and the focus of all political parties has got to be an all-Ireland one and our vision shouldn't be limited to the interests of the southern State. The northern vote must be recognised, promoted and defended, and that the aim has to be to keep the entirety of the island of Ireland in the EU."