By Valentina Pop and  Stephen Fidler

As the U.K. and European Union stake out their positions for negotiations over Brexit, the huge gulf between the two sides is becoming clearer.

Ivan Rogers, Britain’s ambassador to the EU until he left the role last month, told a U.K. parliamentary committee this week the negotiations would be “on a scale that we haven’t experienced, probably ever and certainly since the end of World War II.”

That is quite a task to complete in the two years allotted for negotiations before the U.K. leaves the EU.

Three agreements are supposed to be reached in that time. The first will settle the divorce terms, the second future long-term trade and economic ties and the third the interim arrangements that will get the U.K. from membership to its eventual landing place.

“It’s a fundamental mistake to think there can be three deals in two years. There will be one-and-a-half deals at best,” said a senior EU official.

As a document spelling out the EU’s priorities moves toward completion in Brussels, the British government laid out its negotiating stance in more detail in a white paper published Thursday.

London said it wanted to avoid “a cliff edge for business or a threat to stability, as we change from our existing relationship to a new partnership with the EU.” It also expressed a desire for an agreement about the future partnership after two years and a “phased process of implementation.”

Both sides admit there is no guarantee of any agreement. The white paper restates that Prime Minister Theresa May is ready to walk out, as “no deal for the U.K. is better than a bad deal.” But while diplomats in Brussels aren’t excluding a meltdown in talks, most are convinced that no deal, while bad for both sides, would be worse for the U.K. economy than for the EU’s.

The biggest fight is likely to be over the exit bill the EU expects to deliver to London. That has been estimated in Brussels to be as much as €55 billion to €60 billion (up to $65 billion), computed as Britain’s share of historical commitments made but not paid.

The U.K. has yet to explicitly make its opening response on that debt, but EU officials are expecting it to offer one in the low billions. The white paper projects a narrow vision of what the U.K. intends to pay, saying it will no longer pay for EU projects signed after Nov. 23, 2016, unless they “provide strong value for money and are in line with domestic strategic priorities.”

EU officials admit that the less the U.K. pays, the bigger the fight the remaining 27 will have over money afterwards. But there is strong resistance in the U.K. to paying large sums. You pay money when you join a club, a British lawmaker said this week, not when you leave.

The negotiation’s timing is also prone to sow frustration. After Mrs. May formally notifies the EU of Britain’s intention to leave—possibly as early as March 9—negotiations could start in earnest in June. But progress is likely to be slowed by elections, including in France in May and Germany in September, creating the prospect of what the senior European official called “a big crisis moment” in the negotiations.

Another likely division is over negotiating priorities. For Brussels, settling the divorce is the first priority. In the bloc’s view, transitional arrangements and the future relationship—big issues for Britain, which wants a preferential trade agreement with special arrangements in other areas, such as security, research and transport—will only be completed after the U.K. leaves the bloc.

One area where Mrs. May has the upper hand, however, is over the post-Brexit rights of EU citizens in the U.K., and conversely the rights of Britons living in the EU. An estimated 2.8 million EU nationals reside in the U.K., including 900,000 Poles. In contrast, only about 1 million U.K. nationals live in the rest of the EU, including around 300,000 in Spain.

Mrs. May sought to breach EU’s “no negotiation without [Brexit] notification” stance by offering an early deal on citizens’ status. But the EU countries, fearing side-deals would derail the whole process, insisted this issue be dealt with during the divorce talks.

Still, it is perhaps the priority in the EU, the senior EU official said, providing a strong EU incentive to reach a deal. “If [citizens’] rights are not settled in the divorce deal, the U.K. will unilaterally decide what will happen to them. We will demand reciprocity but I’m not sure we’ll get it,” the official said.

The EU still believes it has the trump cards in the talks. But on questions of money and citizens’ rights, the U.K. has a lot of leverage.