Mr Varadkar's comments will be closely observed by members of Prime Minister Theresa May's Conservative Party who have varied views on how she should deal with the Border question. They were engaged in intense negotiations to close the final differences.
Leading Brexiteer Andrea Jenkyns has restarted her campaign to kick out Mrs May - claiming a leadership election could take just two weeks.
The deal effectively keeps Britain in the EU customs union for the foreseeable future.
However, he warned Mrs May could struggle to get the support of the House of Commons for any agreement she brings back from Brussels.
Tory MP Johnny Mercer said he has received "overwhelming" support from within the party since he described the government as a "shitshow".
"There is an appetite among the majority of the party to pull together because the risks are too high", said another lawmaker who attended the meeting but spoke on the condition of anonymity.
Critics of May used aggressive language in anonymous briefings at the weekend.
Companies will suffer and criminals could benefit from the inevitable border disruption that will ensue if Britain leaves the European Union without a deal, the country's public spending watchdog said on Wednesday.
"What is undoubted and certainly the case is the prospects for an agreement are very adversely effected by the political situation we now see in the UK", Irish Prime Minister Leo Varadkar said this week in Dublin.
"If it is 90 or 95 percent, if there's no solution for the Irish border, for our Parliament it's zero percent that is agreed for the moment".
May has proposed that the whole of the United Kingdom should remain in the EU customs union.
"We need to hold our nerve".
But Brexit minister Suella Braverman said her colleagues were "free to express themselves in the way they wish" and repeatedly refused to say she would back Mrs May in a confidence vote.
Mrs May responded that she did "not want" to extend the transition and saw it as "undesirable".
May's appearance in parliament thus turned into a nationally televised test of her resolve.
MORE than 450 ambulances and fire appliances crossed from Northern Ireland to the Republic to answer emergency 999 calls previous year, it was revealed, as pressure increases against a post-Brexit hard border.
Two key issues remain unresolved in the Brexit talks: how to ensure that the so-called backstop created to avoid a hard border in Ireland has an end point and that it does not allow for Northern Ireland to be separated from Great Britain via a customs border. "They're about the national interest - and that means making the right choices, not the easy ones", May wrote.
Since then, her proposal to extend the transition period has stoked anger among Conservative eurosceptics, who fear she is leading Britain into a deal that will make Britain a "vassal state" indefinitely - unable ever to fully leave the European Union or to forge its own free trade deals with other countries.
"I think if we have some certainty about the next few years when it comes to Brexit, and of course certainty that there won't be a hard border, I think we may then be in a good position to try and get those talks going again".