Brexiteers should be 'ashamed of themselves' for attacks on Theresa May's EU adviser, says head of civil service

'This has to stop. Civil servants have always trusted that our fellow citizens, whatever their views, know that we are doing our duty to implement the decisions of the governments they elect'

Theresa May authorised the letter from the chief of the civil service (Getty)

Brexiteers should be "ashamed of themselves" for briefing attacks against Theresa May's top Europe adviser, according to the UK's most senior civil servant in an extraordinary intervention.

Acting cabinet secretary, Sir Mark Sedwill, made the remarks in a highly unusual public letter in The Times, in reference to recent "anonymous" attacks on Olly Robins and those in the civil service negotiating Britain's exit from the EU.

Highlighting a piece in the same newspaper at the weekend that referred to Mr Robins as the prime minister's "Rasputin", Mr Sedwill said it was now right that his "extraordinary dedication and professionalism" was recognised.

But in the letter, approved by the prime minister, Sir Mark added: "The anonymous sources on whose sniping it also draws on should be ashamed of themselves, especially in a week when another senior civil servant reported having been threatened because of comments about Brexit implementation.

"This has to stop. Civil servants have always trusted that our fellow citizens, whatever their views, know that we are doing our duty to implement the decisions of the governments they elect."

The article from Sir Mark, who is acting cabinet secretary while Sir Jeremy Heywood undergoes cancer treatment, follows months of criticism of Mr Robbins from Brexiteer MPs, who have claimed he is attempting to push for softest possible withdrawal outcome as possible.

Sir Mark later posted a link to the letter on Twitter, saying he had been "defending our Brexit team, and the values of the dedicated and impartial public service of which I'm proud to be a member".

His remarks come after it emerged last week that Jon Thompson, the head of HM Revenue and Customs, had received death threats after revealing the cost of a post-Brexit customs plan advocated by Brexiteers.

Addressing an event at the Institute for Government, Mr Thompson said his comments had "very personal consequences" and that he had to change his travel route. "We have had two death threats investigated by Metropolitan Police for speaking truth unto power about Brexit,' he revealed.