U.K. Prime Minister Theresa May got a first taste of thehigh-wire act involved in European Union negotiations after heropening offer for a Brexit deal ran into immediate opposition fromEU leaders who challenged her attempt to tie a free-trade deal tosecurity cooperation.

In an early sign that two years of divorce negotiations will beas contentious and complicated as feared, Guy Verhofstadt — theEuropean Parliament's point person on Brexit matters and someonewho will have a say on the final outcome — complained that“security is far too important to start to bargain it against aneconomic agreement.”

The slap came hours after May formally served notice that theU.K. will leave the EU in March 2019 and immediately pitched for anunprecedented trade deal that would enable banks to maintain easyaccess to the regional economy. Her government will begin theparliamentary process of taking back control over thousands of EUlaws on Thursday.