THE civil servant leading the UK  Government's planning for a no-deal Brexit has resigned.

Tom Shinner, 33, will leave his role as a director at the Department for Exiting the European Union (DExEU) as the prospect of the UK leaving without a deal increases.

He was tasked with overseeing a smooth Brexit by managing domestic policy implications across government departments.

Tory leadership frontrunner Boris Johnson has said it is "do or die" for Brexit to happen by October 31, although he later insisted the chances of no deal were "a million to one against".

READ MORE: Boris Johnson way ahead of Jeremy Hunt in Tory leadership race

Shinner, director of policy and delivery co-ordination, joined the department in July 2016 and will "hand over after three years in post", DExEU said.

"Careful succession planning has been put in place to ensure the department maintains its high standards of delivery," a spokeswoman added.

It was not said why he was leaving, but a statement said he would leave the civil service to take up a job in the private sector.

READ MORE: Brexit: UK Government stands down civil servants preparing for no deal

He was described as “integral” to Brexit planning by ex-Brexit Secretary David Davis’ former aide, Stewart Jackson.

He wrote in the Times: “There is actually a Mr Big of no deal in Whitehall, very clever and very well paid, who was so integral to the process we joked that if he was hit by a No 53 bus on Parliament Square, Brexit wouldn’t happen!”

His remarks were in reference to Shinner, according to the Guardian.

His resignation follows that of Karen Wheller, the civil servant in charge of “frictionless” post-Brexit border planning, including emergency strategies for Dover and Northern Ireland, from HMRC.

The Institute for Government’s Brexit programme director, Joe Owen, predicted last month that “many of the 16,000 civil servants working on Brexit will now be looking for a change of scenery”.