The Conservative chairman has offered an apology to union bosses after a message was sent out by the party accusing civil servants of being part of an “activist blob”.

The email was sent to supporters last week under the name of home secretary Suella Braverman, claiming an “activist blob of left-wing lawyers, civil servants and the Labour Party” had prevented the government from stopping migrant small boats coming to the UK.

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Both the chiefs of the PCS and FDA unions, which represent civil servants, hit out at the remarks, calling the email a “cowardly attack” that used “disgraceful and disrespectful” language.

And the pair wrote to the prime minister demanding action to be taken against his home secretary.

Now Cabinet secretary Simon Case – the most senior civil servant in Whitehall – has responded to the union chiefs in a letter, seen by Sky News, including an apology from Tory chair Greg Hands.

Mr Case pointed to denials of any involvement by Ms Braverman, saying she had “been clear that she did not see, sign off or sanction the email”.

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‘Government will act now to stop boats’

He revealed the home secretary had written to staff across the department “to thank them for their outstanding work on the Illegal Migration Bill”, and had “made clear her gratitude to Home Office civil servants in her public interviews in recent days”.

But the Cabinet secretary also said he had spoken to party chairman Mr Hands “who apologised for the error”.

Mr Case wrote: “He assured me that he has already taken action to change procedures in CCHQ (Conservative Party headquarters) to make sure that there is not a repeat of this incident.

“Finally, the party chairman has also provided his assurance that attacks on the civil service are not part of any standard CCHQ lines.”

He concluded his letter, saying: “As head of the civil service, I take any instances that may undermine our impartiality incredibly seriously and I am reassured that the error you have raised has been addressed quickly and that actions have been taken to help prevent it happening again.”