U.K. Prime Minister Theresa May vowed to negotiate "the right deal for every single person in this country" as she addressed lawmakers in Parliament just moments after Britain delivered its historic Article 50 exit leader to the European Union.

"We all want to see a Britain that is stronger than it is today. We all want a country that is fairer so that everyone has the chance to succeed," she said in a prepared statement to Parliament. "We all want a nation that is safe and secure for our children and grandchildren."

"We all want to live in a truly Global Britain that gets out and builds relationships with old friends and new allies around the world," May added. "These are the ambitions of this Government's Plan for Britain. Ambitions that unite us, so that we are no longer defined by the vote we cast, but by our determination to make a success of the result."

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May's statement followed the receipt of Britain's formal request to leave the European Union by European Council President Donald Tusk, ending a decades-long membership and triggering a clause in the Treaty of Lisbon that allows member states to negotiate departure.

"There is no reason to pretend this is a happy day", said Tusk in a statement that followed May's address to lawmakers. "There is nothing to win for both sides. This is about damage control. Our goal is clear - to minimise the cost for EU citizens, businesses and member states. We will do everything in our power and we have all the tools to achieve this goal."

"What we should stress today is that, for now, nothing has changed," he added. "EU law will continue to apply to, and within, the United Kingdom."

"For the European Union, the first step will now be the adoption of guidelines for the negotiations by the European Council," it said in a statement on its website. "These guidelines will set out the overall positions and principles in light of which the Union, represented by the European Commission, will negotiate with the United Kingdom."

"In these negotiations the Union will act as one and preserve its interests", the statement added. "Our first priority will be to minimise the uncertainty caused by the decision of the United Kingdom for our citizens, businesses and Member States. Therefore, we will start by focusing on all key arrangements for an orderly withdrawal."