Irish Taoiseach Leo Varadkar | Charles McQuillan/Getty Images Leo Varadkar warns Brexit will haunt UK even after it leaves EU ‘There is no such thing as a clean break. Rather, we just enter a new phase.’

The U.K. will not achieve a "clean-break" Brexit and deep division over the EU will dominate British politics for "many years to come," Irish Prime Minister Leo Varadkar told a business audience in Dublin Thursday.

"The story of Brexit does not end if the United Kingdom leaves on 31st October or even January 31st — there is no such thing as a clean break," Varadkar told the British Irish Chamber of Commerce. "Rather, we just enter a new phase."

Even in the best-case scenario that a deal can be done between London and Brussels, the next phase of agreeing a trade deal will be much harder, he said.

"That will be fraught. There will be difficult debates and even more difficult decisions," said Varadkar, citing a list of issues including tariffs, state aid, visa regimes and aviation landing rights. "I think it may make the negotiations on the Withdrawal Agreement seem simple," he added.

In the scenario of no deal, he said that after a period of living with the consequences, the two sides would need to come back to the negotiating table. But he said the U.K. would not be able to avoid the issues that have dominated the talks for the last two years.

"The first and only items on the agenda for such negotiations will be citizens’ rights, the financial settlement with the EU and a solution to the Irish border," said Varadkar.

"Brexit is not a storm to be weathered," he concluded. "It is a permanent change in the political and economic environment in which the European Union and the United Kingdom will exist."