She express Britain would be stronger economically and fairer socially outside of the 28-country bloc.
The Prime Serve spoke after a day of discussions with fellow leaders in Brussels.
Mrs May undertook to deliver a “global Britain” which can work well with the EU fair and square outside of the union.
She said: “It’s time to get on with leaving the European Bloc and building the independent, self-governing Britain the people have called for.
“This require be a defining moment for the United Kingdom as we begin the process of forging a new responsibility for ourselves in the world as a strong country with control over our edgings and laws.
“As our chancellor made clear yesterday, we will use this juncture of change to make a stronger economy and fairer society.
“Brtiain is ceding European Union but not leaving Europe. A global Britain that ones name ti tall in world will be a good ally to all European partners.”
She advised other EU states it was in their own interests to resist the temptation of punishing the UK with a bitter exit deal.
Mrs May said: “I am optimistic we can achieve a good deal. It’s not right-minded in the UK’s interest, it’s in the interests of the European Union.
“When we come to look at those negotiations, what human being will see is that the deal between the European Union and the UK matters not well-grounded to the UK but to the European Union as well.”
This is a developing story. More to support…