Britain's permanent representative to the European Union Tim Barrow delivers British Prime Minister Theresa May's Brexit letter in notice of the UK's intention to leave the bloc under Article 50 of the EU's Lisbon Treaty to EU Council President Donald Tusk in Brussels, Belgium March 29, 2017.  [Photo/Agencies]

Tusk will reply to the letter within 48 hours and set out a preliminary timetable for the process. The first date on the agenda will be an extraordinary summit of the remaining 27 members of the EU on April 29 where they will decide what they will ask of the UK.

The negotiations will begin sometime after and no one knows how they will progress and what kind of obstacles may emerge, and how all of this will affect the British and European economies.

The British currency has fallen by around 15 percent since voters decided to leave the EU, but the British economy has continued to grow. Chinese investors and officials continue to view the British economy positively and are keen to discuss a free trade deal when Britain has left the EU.

Some banks have already announced their intention to relocate staff from the UK to other EU states but most businesses will wait for greater clarity on the UK's withdrawal before making any decisions. A survey of 222 financial firms by professional services firm EY found that only 23 percent of them were moving staff or considering moving staff because of Brexit.

If negotiations and ratifications do not succeed, Britain could leave the EU without a deal, which most people in Britain fear would be economically disastrous in the short term.

Another option would be a transitional arrangement for up to ten years, in which everything would stay the same to give negotiations more time. The UK can also revoke its decision to leave although that seems unlikely in the current atmosphere.

While May and her ministers appear confident that all will go well for the UK, others are less positive. Michael Heseltine, the former Conservative cabinet minister, told the Guardian the move represented the "worst peacetime decision taken by any modern post-war government. It is what every Conservative prime minister I have worked for was determined to avoid."

There is not much new in the Article 50 letter, said Andrew Neil on the Daily Politics, "but one key point is that the UK has made clear it wants talks on the divorce agreement and a future relationship to be conducted simultaneously.

"This is important because some people in Brussels want the two strands to be separated from each other, which critics say makes an overarching deal less likely."