The European Union has given the go ahead for Brexit trade negotiations to begin next month.
Donald Tusk, the president of the European Council, announced the decision by the EU 27 leaders on Twitter on Friday morning.
At a summit in Brussels, the EU leaders rubber stamped the plan for the UK to be given a 21-month transition period after March 2019.
But the EU is still demanding the UK present a plan for how to avoid a hard border between Northern Ireland and the Republic of Ireland.
Theresa May said said the decision gave “clarity to people and businesses”.
“It gives them the clarity to plan for their future and it ensures that they will only have to make one adjustment, one change, when we enter into the new relationship with the EU in the future,” she said.
“The Council has also endorsed its guidelines for our negotiations for that future relationship. I believe there is a new dynamic in the negotiations.
“I believe we are approaching this with a spirit of co-operation, a spirit of opportunity for the future as well, and we will now be sitting down and determining those workable solutions for Northern Ireland, but also for our future security partnership and economic partnership.
“I believe it is in the best interest of both the UK and the EU that we get a deal that actually is in the interests of both.”
Under the agreed plan, the UK will have to abide by all EU rules until the end of the transition peroid but will not have any say in deciding them.
In exchange, the Britain will be allowed to negotiate new international trade deals during the period at the same time as retaining the benefits of the single market and customs union.
Labour MP Chris Leslie said the prime minister’s so-called “implementation period” was nothing of the sort “because there is nothing implement”.
″All a transition period will do is kick the can down the road on the questions of the Irish border, future trade, security and all the other major decisions that Brexit has thrown up about the future of our country,” the supporter of the pro-Remain Open Britain campaign group said.