Story highlights British official: 'On the threshold of the most important negotiation. .. for a generation'

The EU's 27 member states will need 4-6 weeks to hammer out an initial negotiating position

London (CNN) British Prime Minister Theresa May will trigger Article 50 on March 29, starting official Brexit negotiations between the UK and the European Union, her spokesman has confirmed.

The UK notified the EU on Monday of its intention to invoke Article 50 and will now prepare for a lengthy legislative and political program which promises to be anything but clear-cut.

"Last June, the people of the UK made the historic decision to leave the EU. Next Wednesday, the government will deliver on that decision and formally start the process by triggering Article 50," Brexit secretary David Davis said in a statement Monday.

"We are on the threshold of the most important negotiation for this country for a generation," he added. "The government is clear in its aims: a deal that works for every nation and region of the UK and indeed for all of Europe -- a new, positive partnership between the UK and our friends and allies in the European Union."

In response, Donald Tusk, President of the European Council, tweeted that he would present draft Brexit guidelines to the remaining 27 EU member states withing 48 hours.

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