The "Brexit cruise" didn't get very far. EU leaders drifted down the Danube for an hour, said little about Britain over a leisurely shipboard lunch, then circled back to Bratislava to resume Friday's summit.

Beneath the surface, though, things have been stirring on Brexit. Summit chairman Donald Tusk later stirred them up more by saying Britain's poker-faced prime minister, Theresa May, had let him glimpse her cards, indicating divorce talks prompted by June's referendum may start in four to five months.

Britain's plan to leave the European Union was at the heart of the meeting of the 27 other member states in Slovakia, where May was the notable absentee. But it seemed an empty heart.

Book-ended by talks ashore on repairing the loss of trust in the EU exposed by the British vote, the cruise conversation was minimal, according to Tusk. This left leaders back where they started - waiting for Mrs May and, when the summit ended, bickering with each other over migrants and economics.

Tusk and others repeated their mantra of "no negotiation without notification" - that the EU will not so much as talk to the British until May triggers a two-year countdown to Brexit by formally saying Britain will leave under Article 50 of the EU treaty.

The legal mechanics, written to discourage anyone quitting , mean that triggering it flips negotiating power from London to Brussels by binding Britain to a deadline to strike a deal or lose favoured access to its main export market.

That poses dilemmas for both sides of how much to talk and when. Diplomats speak of a "chicken and egg situation".

Tusk's apparently casual reference to a conversation with May from which he concluded she was "quite likely" to be ready to invoke Article 50 in January or February - a timing she herself is loath to commit to as her government wrestles over strategy - was in line with EU efforts to hurry her along.

PRE-NEGOTIATIONS?

EU officials and governments are keen for Britain be out by early 2019, partly to curb economic uncertainty, partly to avoid a mess if the country is still a reluctant member when the Union chooses a new parliament and executive in mid-2019 and negotiates a seven-year budget to take effect for 2021.

For now, the two sides are entrenched. But there are signs, EU diplomats and officials say, that some discreet talking is getting under way to sound out compromises. Some continental officials told Reuters that they could be open to breaking the current EU embargo on "pre-negotiations" before Article 50.

"We don't mind discussing things informally. We are not dogmatic, we don't feel the need to wait for Article 50," an official dealing with Brexit for an EU government said. "We are friendly towards the Brits and we want to help them along."

For London, an ideal outcome could be to retain free access to EU markets while stopping so many Poles and other EU citizens coming to work in Britain - one of the main demands of the leave side during the referendum campaign. And it would love to reach such a deal before setting the Article 50 clock ticking.

Against this, Brussels is repeating two things: no freedom of access for British goods, services and finance without free movement for EU workers into Britain; and no talks before Article 50 is invoked.

A third mantra is EU unity. If not, as European Parliament speaker Martin Schulz said last week, Britain "would play us off against each other and that would be fatal for the EU".

A mix of fear and admiration for Britain's ability to divide and confuse continentals into webs of shifting alliances appears to be as commonplace in 2016 as it was when French and Germans fumed over "perfidious Albion" two centuries ago: "They have the best diplomats in the world," a senior EU official told Reuters.

"If we don't stick together, they'll eat us alive."

DIFFERENT VIEWS

There are already some differences. Some countries, notably among Britain's northern, free-trading allies, reckon London has to be given some idea of a "landing zone" - what kind of deal it might get - before it hurls itself off the cliff of Article 50.

Others are anxious that Britain would exploit such talks to go on negotiating as much as it could without weakening its hand by starting the two-year clock ticking. They insist on radio silence and hope that demands in Britain itself for faster progress on Brexit will pressure May into action.

Germany is in the former camp for now. The biggest power in the latter is France, which sees pain for Britain as a price worth paying to discourage French voters from taking the Brexit lead and backing Marine Le Pen, leader of the eurosceptic National Front, in April's presidential election.

Paris and Berlin are united, however, in wanting Britain out swiftly, officials say. They accept that May needs time to agree a strategy with a cabinet that includes leading Brexiteers as well as those like herself who campaigned against leaving. But that patience will run out fast after the new year.

"INFORMAL SOUNDINGS"

Some EU diplomats say they have been encouraged by recent contacts. One said British officials had sought "guidelines" on what his country's government might accept, to help London formulate its demands when triggering Article 50. Though "tricky", such informal talks were possible and a fair idea.

British ministers say they are open to informal talks. But a British diplomat denied a campaign of soundings was under way.

A senior official in another major EU country said: "It is still not a coherent, organised attempt to read what would be acceptable. It seems to be rather a lack of ideas in London."

A diplomat from another said: "We are in constant touch with the Brits. But these are not informal negotiations. We just want to help them build a rational negotiating position."

Another, who said he had not been approached, said: "There will have to be informal soundings but it has to be up to the UK first to come up with a sense of what they what they want. Before that it is very difficult to enter into any such conversation. They have to get their own act together first."

As May fills the gaps in her Brexit puzzle, the EU will have to shift gear in response after months of cruising.

Brussels officials will run the negotiations. But Europe's big powers will ultimately be looking after their own interests. Tusk chaired Friday's "Brexit lunch" aboard a German ship, the Regina Danubia - Danube Queen. And when it was over, the EU 27 were led briskly back ashore by German Chancellor Angela Merkel. – Reuters