IRISH Taoiseach Leo Varadkar welcomed yesterday’s agreement, but warned Britain: “This is not the end, it is the end of the beginning.”

Now that phase one, the divorce, is just about done, with the European Commission saying “sufficient progress” has been made, the UK and the EU are preparing for phase two, the future relationship.

This, the Europeans say, is when the hard work really begins.

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There are two parts to phase two: the transition period and the future trade deal.

European Council president Donald Tusk yesterday warned that those trade talks could only be “exploratory”, and a leaked document suggested they were unlikely to start until next February.

Earlier in the day Tusk said he was worried May hadn’t realised quite how difficult trade negotiations would be.

“While being satisfied with today’s agreement, which is obviously the personal success of Prime Minister Theresa May, let us remember that the most difficult challenge is still ahead,” he said. “We all know that breaking up is hard. But breaking up and building a new relation is much harder.

“Since the Brexit referendum, a year and a half has passed. So much time has been devoted to the easier part of the task. And now, to negotiate a transition arrangement and the framework for our future relationship, we have de facto less than a year.”.

The transition, he suggested, will see the UK staying in the single market and customs union and observing all EU laws for around two years after the March 2019 Brexit day.

There is also a wide gulf between what May and her government wants and what the EU, the world’s largest trading bloc, is willing to give.

The Tory leader wants a “close” relationship with Europe, but has “red lines” which may make that tricky.

May, in thrall to the Brexiteers in her party, wants the UK out of the single market, the customs union and the jurisdiction of the European Court of Justice.

She has been accused of cherry-picking and being impractical.

The Europeans want a coherent “end state,” an idea of what Britain wants.

Earlier in the week Chancellor Philip Hammond suggested the Cabinet had not yet properly talked about this.

And reports from Brussels suggest what scant proposals have come from London have so far “not been particularly specific.”

One EU official told a newspaper: “It has been setting out a number of red lines, but what the UK has been saying so far still entails a number of internal contradictions and does not seem entirely realistic to us.”

He added: “I read in the press that the Cabinet has not yet discussed this matter … we need more information from the UK to really be able to engage.”

For the Brexiteers, there are difficulties about how many of Brussels’s rules and regulations the UK will have to keep.

The compromise on the Irish border question means the UK will maintain “full alignment” with elements of the single market if there is no deal.

Tory Leaver David Jones said this would “severely handicap” Britain.