To the Strand Group at King’s College, London, yesterday for the launch of Ian Beesley’s book, The Official History of the Cabinet Secretaries. It was attended by four of five surviving past holders of the office but also, notably, by Sir Jeremy Heywood, the present incumbent.

Sir Jeremy is a remarkable part of what Peter Hennessy used to call the “hidden wiring” of the British constitution, although cabinet secretaries are not so hidden these days. If Boris Johnson had become prime minister, which seemed likely until Michael Gove brought them both down, Sir Jeremy would probably have been out. Dominic Cummings, director of the Vote Leave campaign and former special adviser to Gove, regarded removing the Cabinet Secretary as the condition of a necessary root-and-branch reform of what he regards as a dysfunctional civil service.

Instead, Sir Jeremy is now serving his fourth prime minister, and seems to have become as valuable to Theresa May as he was to David Cameron, Gordon Brown and Tony Blair before her, as Tom McTague of Politico noted yesterday.

Lords Turnbull, Butler and Armstrong, Ian Beesley, Sir Jeremy Heywood, Lord Wilson and Jon Davis. Photo: David Tett

The Cabinet Secretary is the most senior British civil servant, usually head of the Home Civil Service, who sits on the Prime Minister’s right at Cabinet meetings. But the true nature of their job is mysterious, even in today’s era of more open government. So it was interesting to hear from several of the pantheon about what they thought about the job.

Judging by last night’s event, one of the main qualifications for it is the ability to tell well-crafted, diverting and short anecdotes. Lord Armstrong (1979-87) described the job as the “chief engineer of the ship of state”. Lord Butler (1988-98) said the most important thing for ministers was not to dump on civil servants when things go wrong: “When you go tiger-shooting with someone you need to know that when you look round they won’t have gone somewhere else.”

Lord Wilson (1998-2002) agreed that “trust is the key”. He also said was “slightly startled” to see a confidential note he had given Tony Blair had made its way onto the official record (it is in the book). In it, he had warned the Prime Minister not to spend too much time on foreign affairs. Lord Armstrong added that modern travel means that No 10 now has a steady stream of foreign leaders, all of whom expect to see the Prime Minister, and that much of international diplomacy is done leader-to-leader rather than by foreign ministers.

Lord Turnbull (2002-05) said in answer to a question about the role of special advisers that political appointees were a good thing provided relations were good. “I put two very important words into the Special Advisers’ Code: special advisers should not ‘suppress advice’ of civil servants,” he said. “The worst kind of special advisers are those who, in order to maximise their own worth, put themselves in the way and denigrate civil servants.”

Lords Turnbull and Butler. Photo: David Tett

Lord O’Donnell (2005-12) was abroad and so couldn’t attend, but it was a mark of the commitment to open government of the current Cabinet Secretary that he was there to welcome the book as a contribution to the “corporate memory” of the civil service.

He started off by saying, “I’ll do my best to stay out of trouble tonight,” and went on to say that he thought the Prime Minister’s diary was more under control now, and that Lord Wilson’s fears about the Foreign Office filling it had not been fulfilled. On the other hand, it is harder than ever to separate the domestic and the international: national security and Europe being the two main examples.

Asked whether the two new Brexit departments were not bureaucratic make-work schemes, he said he wasn’t going to answer that, before going on to deliver a forceful and succinct defence of Government policy. The Department for Exiting the EU and the International Trade Department were “two wholly new and distinct branches of work”, and it was quite right to establish separate departments to manage them.