The civil service will not be able to implement Brexit while carrying out its other duties after having been shrunk to its smallest size since the second world war, Bob Kerslake, a former Whitehall chief, has warned.

Bob Kerslake calls for fresh referendum on Britain’s membership of the EU

Cabinet secretary Sir Mark Sedwill says emergency contingency plans are needed.

The 2016 referendum, which resulted in a narrow win for those campaigning to leave the European Union, has posed perhaps the most complex set of questions ever faced by a peacetime government.