It's understood Theresa May is going to ask the European Council's president for a short delay to Brexit - rather than a longer one.
The British Prime Minister will write to Donald Tusk later.
The extension she requests is expected to be until the 30th of June - so the UK doesn't have to take part in European elections.
The other 27 EU states are due to meet in Brussels tomorrow.
The UK is scheduled to leave the European Union in nine days.
