Britain will be unable to leave the customs union before 2023, ministers have been told, leading to fears that the delay will be exploited by Remainers to thwart Brexit.

In a briefing to the Cabinet’s Brexit sub-committee earlier this week, senior civil servants said highly complex new technology that will be needed to operate Britain’s borders after Brexit might not be ready for another five years.

Theresa May has asked officials to carry out more work on the two options currently being considered by the Government to replace the customs union - a customs partnership and a so-called “maximum facilitation” plan.

But the expected delays mean that whatever option the Cabinet decides on, the country will have to stay in a form of customs union for four years after leaving the bloc in March 2019.

Brexiteers have expressed serious concerns that Remainers in Parliament will use the delay to try to keep Britain in the customs union and possibly even the Single Market.