Prime Min­is­ter Theresa May for­mally be­gan Britain’s di­vorce from the Eu­ro­pean Union on Wednes­day, de­clar­ing there was no turn­ing back and ush­er­ing in a tor­tu­ous exit process that will test the bloc’s co­he­sion and pitch her coun­try into the un­known.

In one of the most sig­nif­i­cant steps by a British leader since World War Two, May no­ti­fied EU Coun­cil Pres­i­dent Don­ald Tusk in a hand-de­liv­ered let­ter that Britain would quit the club it joined in 1973.

“The United King­dom is leav­ing the Eu­ro­pean Union,” May told par­lia­ment nine months af­ter Britain shocked in­vestors and world lead­ers by un­ex­pect­edly vot­ing to quit the bloc. “This is an his­toric mo­ment from which there can be no turn­ing back.”

The prime min­is­ter, an ini­tial op­po­nent of Brexit who won the top job in the po­lit­i­cal tur­moil that fol­lowed the ref­er­en­dum vote, now has two years to ne­go­ti­ate the terms of the di­vorce be­fore it comes into ef­fect in late March 2019.

newsin­is­de­May, 60, has one of the tough­est jobs of any re­cent British prime min­is­ter: hold­ing Britain to­gether in the face of re­newed Scot­tish in­de­pen­dence de­mands, while con­duct­ing ar­du­ous talks with 27 other EU states on fi­nance, trade, se­cu­rity and other com­plex is­sues.

The out­come of the ne­go­ti­a­tions will shape the fu­ture of Britain’s $2.6 tril­lion econ­omy, the world’s fifth biggest, and de­ter­mine whether Lon­don can keep its place as one of the top two global fi­nan­cial cen­ters.

For the EU, al­ready reel­ing from suc­ces­sive crises over debt and refugees, the loss of Britain is the biggest blow yet to 60 years of ef­forts to forge Eu­ro­pean unity in the wake of two world wars.

Its lead­ers say they do not want to pun­ish Britain. But with na­tion­al­ist, anti-EU par­ties on the rise across Eu­rope, they can­not af­ford to give Lon­don gen­er­ous terms that might en­cour­age other mem­ber states to break away.

Britain’s Prime Minister Theresa May speaks in Parliament as she announces that she has sent the letter to trigger the process of leaving the European Union in London, March 29, 2017. Parliament TV handout via REUTERS

 BREXIT DEAL?

May’s no­tice of the UK’s in­ten­tion to leave the bloc un­der Ar­ti­cle 50 of the EU’s Lis­bon Treaty was hand-de­liv­ered to Tusk in Brus­sels by Tim Bar­row, Britain’s per­ma­nent rep­re­sen­ta­tive to the EU, on the top floor of the new Eu­ropa Build­ing in Brus­sels, ac­cord­ing to a Reuters pho­tog­ra­pher in the room.

That mo­ment for­mally set the clock tick­ing on Britain’s two-year exit process. Ster­ling, which has lost 25 cents against the dol­lar since the June 23 ref­er­en­dum, jumped to $1.25.

May signed the 6-page Brexit let­ter on Tues­day night, pic­tured alone at the cab­i­net table be­neath a clock, a British flag and an oil-paint­ing of Britain’s first prime min­is­ter, Robert Wal­pole.

Her let­ter sought to set a pos­i­tive tone for the talks though it ad­mit­ted that the task of ex­tract­ing the UK from the EU was mo­men­tous and that reach­ing com­pre­hen­sive agree­ments within two years would be a chal­lenge.

May wants to ne­go­ti­ate Britain’s di­vorce and the fu­ture trad­ing re­la­tion­ship with the EU within the two-year pe­riod, though EU of­fi­cials say that will be hard given the depth of the re­la­tion­ship.

“We be­lieve it is nec­es­sary to agree the terms of our fu­ture part­ner­ship along­side those of our with­drawal from the EU,” May told Tusk in her let­ter, adding that Lon­don wanted an am­bi­tious free trade agree­ment with the EU.

“If, how­ever, we leave the Eu­ro­pean Union with­out an agree­ment the de­fault po­si­tion is that we would have to trade on World Trade Or­ga­ni­za­tion terms,” she said.

Protesters gather outside Parliament after Britain’s Prime Minister Theresa May triggered the process by which the United Kingdom will leave the European Union in London, March 28, 2017. REUTERS/Stefan Wermuth

TRADE AND SE­CU­RITY

May has promised to seek the great­est pos­si­ble ac­cess to Eu­ro­pean mar­kets but said Britain was not seek­ing mem­ber­ship of the ‘sin­gle mar­ket’ of 500 mil­lion peo­ple as she un­der­stood there could be no “cherry pick­ing” of a free trade area based on un­fet­tered move­ment of goods, ser­vices, cap­i­tal and peo­ple.

Britain will aim to es­tab­lish its own free trade deals with coun­tries be­yond Eu­rope, and im­pose lim­its on im­mi­gra­tion from the con­ti­nent, May has said.

In an at­tempt to start Brexit talks on a con­cil­ia­tory note, May said she wanted a spe­cial part­ner­ship with the EU though she laced that am­bi­tion with an a clear link­age of the eco­nomic and se­cu­rity re­la­tion­ship.

EU lead­ers will wel­come as­sur­ances of a con­struc­tive ap­proach and ap­pre­ci­ate a com­mit­ment to re­main a close part­ner for the EU and to en­cour­age its de­vel­op­ment, as well as an ex­plicit recog­ni­tion that Britain can­not re­tain the best bits of mem­ber­ship af­ter leav­ing.

They may be less warm to an im­pli­ca­tion that Britain could live with a break­down of talks on trade cou­pled with what might be seen as a threat to dis­rupt the se­cu­rity and counter-ter­ror­ism co­op­er­a­tion for which Britain, as a mem­ber of the U.S.-backed An­glo­phone Five Eyes sys­tem, is highly val­ued.

“We should work to­gether to min­i­mize dis­rup­tion and give as much cer­tainty as pos­si­ble,” May said. “Weak­en­ing our co­op­er­a­tion for the pros­per­ity and pro­tec­tion of our cit­i­zens would be a costly mis­take.”

Tusk said the EU would seek to min­i­mize the cost of Brexit to EU cit­i­zens and busi­nesses and that Brus­sels wanted an or­derly with­drawal for Britain.

“We al­ready miss you,” said Tusk who will send the 27 other states draft ne­go­ti­at­ing guide­lines within 48 hours. “Thank you and good­bye.”

Ger­many will strive in Brexit ne­go­ti­a­tions to make sure there is as lit­tle dis­rup­tion as pos­si­ble to the lives of Eu­ro­pean Union cit­i­zens liv­ing in Britain, Chan­cel­lor An­gela Merkel said.

Stress­ing that she hoped Britain and the EU would re­main close part­ners, Merkel said the prospect of Brexit made many peo­ple in Eu­rope wor­ried about their own per­sonal fu­ture.

“This is the case es­pe­cially for the many Ger­mans and Eu­ro­pean cit­i­zens in Britain. There­fore, the Ger­man gov­ern­ment will work in­ten­sively to make sure the ef­fect on the every­day lives of those peo­ple is as small as pos­si­ble,” she said.

The Big Ben clock tower is seen in London, Britain March 29, 2017. REUTERS/Hannah McKay

TWO YEAR BREXIT

But the course of the Brexit talks – and even their scope – is un­cer­tain.

“The time-frame is damn nar­row,” said Mar­tin Schae­fer, a spokesman for the Ger­man For­eign Min­istry.

In re­cent months, Ger­man of­fi­cials have made clear that they do not be­lieve there is time to ne­go­ti­ate a be­spoke tran­si­tional agree­ment for Britain that would come into force im­me­di­ately af­ter Brexit.

A huge num­ber of ques­tions re­main, in­clud­ing whether ex­porters will keep tar­iff-free ac­cess to the sin­gle mar­ket and whether British-based banks will still be able to serve con­ti­nen­tal clients, not to men­tion im­mi­gra­tion and the fu­ture rights of EU cit­i­zens in the UK and Britons liv­ing in Eu­rope.

One ma­jor un­cer­tainty for May is who will be lead­ing France and Ger­many, which both face elec­tions this year.

“It’s bad news for every­body. It’s a wedge pushed into the Eu­ro­pean pro­ject,” said French cen­trist pres­i­den­tial can­di­date Em­manuel Macron, who has made clear he would en­sure Britain gains no un­due ad­van­tages out­side the Union.

UNITED KING­DOM?

At home, a di­vided Britain faces strains that could lead to its break-up. In the Brexit ref­er­en­dum, Eng­land and Wales voted to leave the EU but Scot­land and North­ern Ire­land voted to stay.

Scot­tish na­tion­al­ists have de­manded an in­de­pen­dence ref­er­en­dum that May has re­fused. In North­ern Ire­land, ri­val par­ties are em­broiled in a ma­jor po­lit­i­cal cri­sis and Sinn Fein na­tion­al­ists are de­mand­ing a vote on leav­ing the UK and unit­ing with the Re­pub­lic of Ire­land.

May said she knew that trig­ger­ing Brexit would be a day of cel­e­bra­tion for some and dis­ap­point­ment for oth­ers.

“Now that the de­ci­sion to leave has been made and the process is un­der way, it is time to come to­gether,” she said.