Speaking after London announced that Prime Minister Theresa May would start the two-year withdrawal process by writing to European Union summit chair Donald Tusk next Wednesday, the source said this did not leave enough time to convene the other 27 leaders on April 6-7, dates that had been penciled in for a meeting.
Although Britain as a whole voted 52-to-48 in favor of leaving, majorities of voters in both Scotland and Northern Ireland favored staying in the European Union.
Opposition Labour leader Jeremy Corbyn said his party accepted the Prime Minister had a mandate to start the process of leaving the EU.
Mr Margaritis Schinas, spokesman for EC chief Jean-Claude Juncker, said: "Everything is ready on this side".
"It's fascinating that the pound sunk quite so quickly as we knew the end of March was the preferred date".
Mrs May is expected to make a statement to the House of Commons on Wednesday shortly after invoking Article 50, setting out her aims.
The prime minister has said that "now is not the time", and is expected to visit Scotland as part of a pre-Brexit tour of Britain that began on Monday in Wales and will also take in Northern Ireland. We want negotiations to start promptly.
A response from the group is expected in around 48 hours after the UK's notification, according to European Commission negotiator Michel Barnier.
Triggering Article 50 will mark the beginning of two years of negotiations, with a spokesperson for the Prime Minister stating that Theresa May is confident talks will stick to a two-year timeline.
Reacting to the confirmation of the date, Karen Briggs, head of Brexit at KPMG said, "Although the UK's substantial financial contribution to the European Union and its status outside the Schengen Area offer the opportunity for a unique deal to be struck, businesses still need to plan for a "no deal" scenario".
"I have set out my objectives".
Mr Farron repeated his call for voters to have the final say on the deal negotiated by Mrs May, arguing that departure from the European Single Market was not on the ballot paper in June.
The PM promised to work on a deal "that works for everyone across the United Kingdom and all parts of the UK".
David Davis, the secretary of state for exiting the European Union, said: "Last June, the people of the United Kingdom made the historic decision to leave the EU".
Brexit minister David Davis has said there would be no sudden drop in numbers, as it would take years to fill low-skilled jobs in hospitality, social care and agriculture now done by immigrants.
May and European Union leaders say transitional arrangements may well be needed, to give more time to agree a future trade deal and give people and businesses time to adjust to the divorce.