LONDON: Britain sought to downplay a row over future security ties with the EU on Thursday, as London and Brussels drew up the first battle lines at the start of their two-year divorce.
France and Germany also put up a common front against Prime Minister Theresa May's call to negotiate the exit and the new relationship at the same time, setting up a major stumbling block before negotiations even begin.
But a day after May formally notified the EU of Britain's intention to leave, it was her warning that failure to clinch a deal on trade would weaken the fight against terrorism that rankled.
"It's not a threat," Brexit minister David Davis told BBC radio after warnings from Brussels against using security as a bargaining chip in the talks.
He said the "simple truth" was that without a "parallel deal" with the EU, Britain would no longer be a member of the Europol crime-fighting agency or take part in the European Arrest Warrant system.
Interior minister Amber Rudd said Britain was the top contributor to Europol, adding: "If we left Europol, then we would take our information... with us".
The European Parliament's chief Brexit negotiator, Guy Verhofstadt, said that "citizens' security was far too serious a subject" to be held hostage to negotiations.
Sylvie Bermann, France's ambassador to Britain, echoed that sentiment, telling the BBC that there "can't be a trade-off" between trade and security.
"I don't understand that because it wouldn't be in the interest of the UK because we're all facing the same security challenges," she said.
- Exit deal first -
The row came as some of the EU's top leaders fleshed out their strategy for the hard talks ahead as the bloc reels from the blow of one of its biggest members becoming the first state ever to start withdrawal from the 60-year-old union.
The path ahead is strewn with obstacles.
French President Francois Hollande on Thursday followed German Chancellor Angela Merkel in rejecting May's proposed structure for the negotiations, saying the exit agreement should come first.
"First we must begin discussions on the modalities of the withdrawal, especially on the rights of citizens and the obligations arising from the commitments that the United Kingdom has made," Hollande said.
"On the basis of what progress is made, we could open discussions on the framework of the future relations between the United Kingdom and the European Union."
The fate of three million EU citizens living in Britain and one million British people within the bloc's nations is at the top of leaders' agenda.
Also looming large is the so-called "exit bill" Britain will have to pay, estimated to be as much as 60 billion euros ($64 billion, £52 billion).
In the first business fall-out since May's Brexit notification, the prestigious Lloyd's of London insurance market said it would open a new Brussels subsidiary to ensure smooth operations in the EU.
Several banks have announced plans to increase operations in continental Europe as a safeguard once Britain leaves the single market.
British business leaders are also increasingly alarmed about a "cliff edge" scenario in which Britain leaves the European bloc with no deal.
Before the talks can even get under way, the government on Thursday will outline plans for the daunting task of amending or scrapping EU regulation as it is brought into British law.
- 'See EU soon' -
Analysts said the tone of Wednesday's historic announcement and the EU's initial reaction was largely conciliatory except for the warning on security.
In a letter setting out Britain's position, May stressed she wanted to forge a "deep and special relationship" with the rest of the bloc.
Tusk is due to issue draft "negotiating guidelines" on Friday and leaders of the 27 remaining EU countries will hold a special summit on April 29 to rubber stamp the plans.
While the bloc has tried to show a united front in the face of Brexit, celebrating the EU's 60th anniversary earlier this month, in Britain the prime minister is struggling to unite her own country.
Britons last year voted 52 percent to 48 percent in favour of Brexit after a bitterly divisive campaign.
The referendum result has also led to a renewed campaign for independence in Scotland, after a majority of Scots voted for Britain to stay in the EU in the June referendum.
"Dear Donald Tusk, We'll see EU soon" read Thursday's headline of Scotland's pro-independence newspaper, The National.