Theresa May has been warned she is sabotaging the UK’s preparations for Brexit by reshuffling ministers too often.

The respected Institute for Government (IfG) think-tank has calculated that only David Davis and one other minister, Robin Walker, have remained in place since the Department for Exiting the European Union (DExEU) was created in 2016.

And the department’s minister in the Lords, who has a crucial role in shepherding contentious Brexit legislation through the Upper House, has changed three times.

Half of DExEU’s ministers changed at the June 2017 reshuffle.

However the ministerial team did remain in tact at May’s January 2018 shake-up and the department actually gained a minister.

The National Audit Office reported that DExEU’s staff turnover is 9% a quarter, when most departments average 9% a year.

The IFG also warned the prime minister she will have a tougher time pushing through her Brexit legislation than needed due to “a high level of turnover in the Commons Whips’ Office”

There have been two chief whips and three deputy chief whips since November 2017. More than 70% of whips were new to their posts following the January 2018 reshuffle.

Labour MP Stephen Doughty said the report showed Brexit was “clogging up the pipes of Government like the world’s largest fatberg, preventing anything else from getting through”.

“The key department responsible for delivering Brexit is in turmoil, with a staff turnover rate far above the average. This is not surprising considering hard-working civil servants are being asked to do the impossible by the hard Brexit fanatics in Government,” he said.

“Important projects and legislation are now bogged down in the knee-deep mud of Brexit, which is turning out to be much more complicated than anyone could have known during the referendum. As the vision of Brexit sold to the British public becomes increasingly undeliverable, people have every right to keep an open mind about whether it’s the right path for the country.”

Gavin Freeguard, the associate director of the IfG who wrote the report published today, said: “New ministers will need to get up to speed quickly to face the challenges in public services, major projects and Brexit.