Leo Varadkar has warned the UK that the EU will have the upper hand in post-Brexit trade talks.
He warned that the bloc has a “stronger team” because of its far larger population and market in comparison.
Mr Varadkar also suggested that Prime Minister Boris Johnson may run out of time to get a trade deal signed before the end of the year when the transition period finishes.
The Taoiseach, who is fighting a general election, spoke to the BBC ahead of meeting with the EU’s chief negotiator, Michel Barnier, in Dublin.
“The European Union is a union of 27 member states. The UK is only one country. And we have a population and a market of 450 million people,” Mr Varadkar said.
“The UK, it’s about 60 (million). So if these were two teams up against each other playing football, who do you think has the stronger team?”
Mr Johnson has repeatedly ruled out requesting an extension to the transition period, during which the UK abides by EU rules, past December 31.
But Mr Varadkar, whose talks with the PM were seen as key in securing a breakthrough on the exit pact, questioned whether it would be possible to negotiate a full trade deal in time, saying “it will be difficult to do this”.
He did however pledge to work “night and day” to try and get it done and said “we won’t be dragging our feet’”.
However he warned against any attempt by the UK to broker parts of a deal over time with the EU.
“When I hear people talk about piecemeal, it sounds a bit like cake and eat,” he said.
“That isn’t something that will fly in Europe.”
Mr Varadkar explained that there were fears in the EU that the aim of Brexit was to undercut standards and that it was still up to the UK to make those assurances.
Mr Johnson has repeatedly insisted that there would be no lowering of standards in the event of a trade deal with the US and UK but the EU will insist on alignment if there is to be a close trade deal.
He said: “There’s a genuine concern across the European Union, that part of the motivation behind Brexit was for the UK to undercut us in terms of environmental standards, labour standards, product standards, food standards, all of those things.
“Now when I meet Prime Minister Johnson he says, no absolutely not that’s not the kind United Kingdom that I want to need as prime minister.
“But we want that written down in law, we want that in a treaty so that we know that the UK will not be undercutting the EU with lower standards.”
He said that a lot of people “unfortunately in Westminster, and in Britain, don’t understand Ireland or know much about Ireland” which had led the UK to underestimate how important it was for Dublin to prevent a hard border.
He explained: “That’s one thing that we actually find hard to understand because, you know if you grow up in Ireland, you know, we speak English as our first language, most of us do anyway.
“We watch the BBC, you know, we watch Graham Norton, we watch your television, your news.
“We really understand a lot about Britain, but I think a lot of British people don’t understand a lot about Ireland, including your politicians.
“And that’s what was very badly exposed I think during the whole Brexit process.
“And politicians in Westminster had to learn more about Ireland.
“And I think as they learned they started to understand these issues, how sensitive the political situation is in Northern Ireland, and how we could never countenance a return to a hard border and how that was more important to us than economic issues.”
Mr Varadkar said Britain’s colonial history may have led politicians to misunderstand the way the EU worked in the 21st century.
“I think a lot of British people don’t understand a lot about Ireland, including your politicians, and that is what was very badly exposed during the whole Brexit process,” he said.
“Britain has a very powerful history, it is a very colonial history. I think there are people in Britain who thought that France, Germany and Britain would get together at a big summit and tell the smaller countries what’s what.
“That is not the way the 21st century works.”
Mr Varadkar said he had been genuinely afraid that the UK might have left the EU without a deal, but that a meeting between the two men on the Wirral in the autumn had provided the “crucial moment”.
He said the progress at the summit was the “simple story” of “two guys in a room… talking turkey” without their staff present, where they found a way that they could move forward.
“I knew when I was leaving Liverpool Airport that things were looking promising again”, he said.