Former Whitehall chief Gus O’Donnell has stepped up his criticism of politicians accusing civil servants of bias over Brexit, arguing their attacks amounted to bullying.
Independent crossbencher Lord O’Donnell, who headed the civil service for six years, also warned that it was damaging to democracy.
His comments came amid a continuing row over Treasury forecasts which showed Britain would be worse off after Brexit whatever the outcome of negotiations.
Jacob Rees-Mogg, who chairs the influential European Research Group of backbench Hard Brexiteers, has stood by his claims that officials had been “fiddling the figures”.
Brexit minister Steve Baker was forced to apologise in the Commons for remarks he made about the impartiality of the civil service.
At the weekend, Lord O’Donnell described Brexiteers as “snake oil” salesmen who “don’t like the idea of experts testing your products”.
Speaking during a private notice question in the House of Lords about “unwarranted” criticism of the civil service, Lord O’Donnell said: “Does the minister believe that those making allegations without supporting evidence against serving civil servants who will not respond are undertaking a form of bullying?
“That to be honest is something which actually diminishes those making the attacks, but I think more importantly damages our democracy.”
Responding, Government frontbencher Lord Young of Cookham said: “Whether the accusations made in the House of Commons constitute bullying, I am not quite so sure.”
But he added: “I think that they were ill-advised given that the evidence did not stack up the accusations that were made.
“The people who come out of it worse are the those who make the accusations rather than those that they were levied against”.
Tory peer Lord Tugendhat argued those politicians who impugned the impartiality of civil servants were “behaving very much as President Trump does in the United States with regards to the FBI”.
Lord Young, triggering laughter among peers, said: “I am not sure I want to open up a fresh front from the despatch box.
“President Trump I hope will read what he has just said.”
Whitehall historian and independent crossbencher Lord Hennessy of Nympsfield recalled the post-war chancellor Hugh Dalton, on receiving unwelcome advice, had described his official as “contemptible snag-hunters”.
“But surely that’s what we pay them for?”, he added.
Lord Hennessy argued a politicised civil service would be “ruinous for this country”.
Lord Young agreed and said: “It is the job of civil servants to bring to ministers’ attention the consequences of their policies, to argue forcibly against them if they believe they are misguided, but once the decision has been taken to go out and deliver them as best they can.”
The question had originally been asked by opposition spokesman Lord Hunt of Kings Heath, who hit out at the “disgraceful slurs” made against officials.
Lord Young, who has held numerous senior posts in government, said: “I have never had occasion to question the impartiality or the objectivity of civil servants. They have spoken truth unto power.
“Quite often they have said things that I didn’t want to hear, but I would never accuse them of some of the accusations that have recently been levied against them.
“I think we should be proud of our civil service and I reject the smears that have been made against them.”
But Tory peer Lord Blencathra, the former MP David Maclean, highlighted the Treasury analysis produced ahead of the 2016 referendum that forecast “the complete collapse of the British economy if we were to vote to leave”.
He said: “I have maintained this document was propaganda from top to bottom as it turns out to be untrue in reality.”
He added: “If I continue to criticise the mandarins and the ministers who approved the statistics and this document, does that make me a snake oil salesman or a 1930s German Nazi?”
Lord Young said there was a need to distinguish between criticism of ministers and civil servants.
He said the document had been presented by the then chancellor and added: “Any criticism should be directed at the politicians who presented it…they are the ones who should be criticised rather than the civil servants.”