Meanwhile, it was reported that representatives from Scotland, Wales, and Northern Ireland only heard about the Article 50 trigger date from the media. Crucially, it has never been tested before because no member has ever left the EU.
No details of the letter submitted to Tusk's office were disclosed.
The two-year process of Britain formally leaving the EU will get underway at the end of the month but exit talks between May's government and European leaders aren't expected to begin for another two months. Even Davis is readying for what "may be the most complicated negotiation of all time".
Mr Davis told the House of Commons Brexit Select Committee he was not yet able to "quantify" the impact of no Brexit deal being made.
The news came one week after Parliament passed the Brexit Bill, with MPs overturning amendments aimed at guaranteeing the rights of European Union citizens in the United Kingdom, and four days after the Queen gave her royal assent.
"For nine months since the European Union referendum, there has been no attempt by the United Kingdom government to seek a meaningful discussion or agreement with the devolved administrations".
The European Commission's Brexit negotiator Michel Barnier has said they must be wrapped up by October 2018 to give the EU and national parliaments time to ratify the deal. She campaigned to remain in the European Union but must now navigate the exit, after succeeding David Cameron, who resigned when he lost the referendum. Britain's economy is already at risk because of uncertainty over the country's future, so prolonging that uncertainty is a problem.
May's preparations for Brexit have been hit by Scottish First Minister Nicola Sturgeon's announcement last week that she planned a new independence referendum in order to keep European Union ties.
Both sides would like the early resolution of the status of more than three million Europeans living in Britain, and more than one million Britons living elsewhere in the EU. A worst case would see the talks break down prematurely.
May's team has questioned the size of the bill and how much legal obligation Britain is under to pay it. "It also acts as a reminder that the next two years will likely continue to be volatile for the UK currency as well as the FTSE and UK Gilts, with traders still concerned about the road the country is on".
Stephen Gethins, the SNP's Europe spokesman, said: "Today's announcement that the Prime Minister will push ahead and unilaterally trigger Article 50 shatters beyond fix any notion or position that the Prime Minister is seeking a UK-wide agreement".