The head of the civil service, Mark Sedwill, has taken the highly unusual step of emailing staff across Whitehall to try and put an end to the "recent stories of tensions". It follows last week's report in the Times that Priti Patel was presiding over an "atmosphere of fear" at the Home Office. Despite a show of unity yesterday, Patel is thought to be at loggerheads with her permanent secretary Philip Rutnam, who reportedly suggested that the timescale for her points-based immigration system was unrealistic.

What Sedwill's letter confirms is that the Home Office is not the only ministry where civil servants are feeling under the cosh. There have been rumours for some time of an uncompromising and forceful management style from other senior members of Johnson's cabinet. With relatively low pay compared to the private sector, the civil service's staff turnover has already been rising due to the stresses and strains of Brexit according to the Institute for Government. Overly demanding bosses might push some over the edge.

But this is exactly what Dominic Cummings and his crew in the Cabinet Office want. Cummings has long been critical of what he terms "the blob" (the establishment in general, and the civil service in particular) and last month's job advert for "assorted weirdos" was an attempt at bypassing the civil service's strict hiring process.

Fundamentally, the government thinks that it cannot force through its agenda without removing from the civil service certain senior figures whom they believe are inimical to Brexit. Hence the instant replacement of Olly Robbins with David Frost as the government's chief negotiator when Johnson became prime minister last July. Philip Rutnam at the Home Office, Tom Scholar at the Treasury and Simon McDonald at the Foreign Office are all thought to be in the firing line.

But Johnson and Cummings will quickly learn that civil service reform takes time, money and effort. The coalition government expended much energy trying to enact Francis Maude's recommendations to reduce the size of the civil service by 23 per cent. A 19 per cent reduction was achieved, only for the experiment to come crashing to a halt in 2016. The number of civil servants has been growing steadily ever since.

History teaches us that Whitehall is not a blob, but a many-headed hydra. Cut staff in one place and they will grow back elsewhere. It will be interesting to see how long the government's appetite for eternal battle lasts.