Civil servants were ordered to 'tone down' their enthusiasm when welcoming Labour ministers into Whitehall's departments on Friday, The Mail on Sunday has learned.
Before their newly appointed political bosses arrived, officials received instructions not to cheer or 'clap too loudly' – to avoid the 'appearance of bias' for Labour.
The revelation will give credence to long-held grievances by the Tories that sections of the Civil Service were politically opposed to the Conservative Government.
It comes amid claims that mandarins have been underwhelmed by Labour's readiness for office, and that Sir Keir Starmer's chief-of-staff Sue Gray 'doesn't like things written down'.
Following Labour's election victory, the freshly promoted Secretaries of State called in to their new departments to meet their permanent secretaries and staff.
At the Treasury, incoming Chancellor Rachel Reeves – the first woman to hold the post – was given what one observer described as 'rock-star treatment'.
Pictured: Chancellor Rachel Reeves arrives at the Treasury on July 5
At the Treasury, incoming Chancellor Rachel Reeves – the first woman to hold the post – was given what one observer described as 'rock-star treatment'
But in other Whitehall departments, staff were told to 'tone down' their greetings.
An insider said: 'Welcoming is one thing, but betraying over-the-top partisan support is quite another. You can understand the emotion as Rachel Reeves arrived at the Treasury, but it was a bit Taylor Swift.'
Last night Cabinet Office sources said they were 'not aware of any central directive' for the ministerial greetings, but added that it was 'customary for incoming ministers to be welcomed into their departments by their permanent secretaries'.
Separately, Gary Gibbon, the political editor of Channel 4 News, revealed how civil servants who had been involved in pre-election 'access talks' between Labour politicians and civil servants, 'aren't universally awed by Labour's preparations'.
He reported mandarins' concerns that 'there doesn't seem to be a sort of brains trust always at the top of Labour policy areas, ready to come in and do the sort of heavy lifting that normally happens'.
Pictured: Sue Gray arrives at the Covid Enquiry on May 16 in Belfast
The HM Treasury building in London pictured on the left
Mr Gibbon added: 'They also talk about the chief-of-staff Sue Gray – a civil servant whom we got to know so well over Partygate. She's been liaising quite a lot with the Civil Service and she has a very particular modus operandi.
'She goes in – and she's always done this in every job you ever hear of – and doesn't like things being written down.
'Now, if you're trying to approve a 28-point plan for how on earth you're going to repair some major part of the public infrastructure or something, well, it kind of helps, probably, if you write it down.'
However, the new PM insisted yesterday that Labour had made 'extensive' preparations for power to ensure 'we can hit the ground running'. The Government was approached for comment.