The European Union will be ready to respond within 48 hours to Britain's notification that it plans to leave the 28-nation bloc, the chairman of EU leaders, Donald Tusk, said on Friday.

Britain has said it will submit its formal notification to exit the EU by the end of March following last summer's referendum. Some diplomats expect it to come as early as next week.

The notification would trigger a legal process lasting two years during which London would negotiate the terms of the divorce. British Prime Minister Theresa May hopes that time can also be used to discuss future trade and other relations.

"We are well prepared for the whole procedure and I have no doubt that we will be ready within 48 hours, I think it is a proper time to react," Tusk told a news conference.

German Chancellor Angela Merkel said that, depending on the exact timing of the British notification, EU leaders would organise a special summit, at which they would agree broad negotiating guidelines for the European Commission to conduct the divorce talks with London.

"If the letter comes next week, the special summit will be on April 6," Merkel told a news conference.

"If it comes later than next week then we'll have to find a date after April 6. We are fully prepared and we will wait with interest. But on which day it will come in March is not of such great significance," she said.

Irish Prime Minister Enda Kenny told reporters the April 6 special summit could take place of Britain submited its notification by March 15.

EU leaders could then issue within 48 hours the guidelines for the negotiations with Britain.

"There would be guidelines issued by the European Council within 48 hours and the European Council meeting to adopt those guidelines will be on April 6," Kenny said.