Smooth orderly Brexit in interests of all: British PM Theresa May

London: British Prime Minister Theresa May today called for a Brexit that is as "smooth and orderly" as possible.

Speaking in Brussels at the start of a European Union (EU) summit, May also reiterated her plan to trigger Article 50 of the Lisbon Treaty to start the official exit process by March 2017.

"We are leaving the European Union. We want that to be as smooth and orderly a process as possible. It is not just in our interests, it is in the interests of Europe as well," she said.

"We are going to invoke Article 50, trigger the negotiations by the end of March next year and it is right that the other leaders prepare for those negotiations as we have been preparing," she added.

EU leaders from all 28 member states, including May, will discuss a series of issues, from how to deal with Russia over Ukraine and Syria to fraught relations with Turkey.

The British premier however, is not invited to an informal working dinner this evening where the 27 other representatives hold strategic talks.

European Council President Donald Tusk has reportedly specifically altered the traditional summit format in order to arrange the exclusion of Britain from the evening event, given his stand that Britain cannot be part of Brexit talks until it has invoked Article 50.

Meanwhile, the UK ambassador to the EU, Ivan Rogers, is reported to have privately told the British government that a Brexit deal might not be done until the early to mid-2020s.

He also cautioned that an agreement could be rejected ultimately by other EU members' national parliaments.

"It is wrong to suggest this was advice from our ambassador to the EU. Like all ambassadors, part of his role is to report the views of others," a Downing Street spokesperson said.