Britain may remain a member of the European Union (EU) until 2019, a year longer than previously estimated, a media report on Sunday said.
Prime Minister Theresa May has been expected to enact Article 50 of the Lisbon Treaty in January 2017, setting in motion the formal two years of negotiations before Brexit.
However, she may be forced to delay it because her new Brexit and international trade departments will not be ready, the Sunday Times quoted sources as saying.
French and German elections are also being cited as a cause for delay.
Britain might not invoke Article 50 until France has voted next May or until after the German poll in September.
A UK cabinet minister has also reportedly confirmed to the Sunday Times that there were "some challenges" in the French and German electoral timetables.
David Davis, secretary for Exiting the European Union, and Liam Fox, the international trade secretary, had indicated after May appointed them that they expected Britain to leave at the start of 2019.
However, their new government departments are being set up from scratch and the situation is reportedly "chaotic".
Another senior government insider told the newspaper there was uncertainty about preparatory talks with EU leaders, in which Britain would try to reach understandings on key issues before triggering Article 50.
"The prime minister has been clear that a top priority for this government is to deliver the decision of the British people to leave the EU and to make a success of Brexit. The PM has set out the government’s position on Article 50 and has established a new department dedicated to taking forward the negotiations," said a Downing Street spokesperson.