Updated March 29, 2017 12:47:28

Photo: Theresa May's signing of Article 50 of the EU Lisbon Treaty officially triggers the Brexit process. (Reuters: Christopher Furlong)

British Prime Minister Theresa May has officially triggered the Brexit process by signing Article 50, pitching the United Kingdom into unknown territory following a June 2016 referendum that voted to leave the European Union.

Ms May is expected to file the formal divorce papers to EU Council President Donald Tusk on Wednesday evening (Australian time).

After filing the papers, Ms May — an initial opponent of Brexit who won the top job in the political turmoil that followed the referendum vote — will have two years to settle the terms of the divorce before it comes into effect in late March 2019.

"Now that the decision has been made to leave the EU, it is time to come together," Ms May said, according to comments supplied by her office.

"When I sit around the negotiating table in the months ahead, I will represent every person in the whole United Kingdom — young and old, rich and poor, city, town, country and all the villages and hamlets in between."

On the eve of Brexit, Ms May, 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 a host of other complex issues.

What will be the short-term damage when the United Kingdom leaves the EU single market?

The outcome of the negotiations will shape the future of Britain's $3.4 trillion economy, the world's fifth biggest, and determine whether London can keep its place as one of the top two global financial centres.

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 devastating world wars.

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

Within 48 hours of reading the letter, Mr Tusk will send the 27 other states draft negotiating guidelines. He will outline his views in Malta, where from Wednesday he will be attending a congress of centre-right leaders. Ambassadors of the 27 will then meet in Brussels to discuss Mr Tusk's draft.

The course of the Brexit talks is uncertain.

Wires/ABC

Topics: world-politics, government-and-politics, united-kingdom, european-union

First posted March 29, 2017 10:14:21