Britain could remain in the EU until late 2019, almost a year later than predicted, ministers have privately warned senior figures in the City of London.

Theresa May has been expected to enact article 50 in January, setting in train the formal two years of negotiations before Brexit.

Despite great political pressure to stick to that timetable, she may be forced to delay because her new Brexit and international trade departments will not be ready, City sources said.

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 even until after the German poll in September, ministers confided to senior City contacts.

“You can’t negotiate when you don’t know