So why didn’t they say something at the time? In their retirement there is a procession of top government officials ready to tell us that the decision to invade Iraq was a disaster. The latest is Sir Jeremy Greenstock, the UK Ambassador to the UN in the run-up to the war. A thoroughly decent and thoughtful man his views were always listened to carefully by anyone in government.
But when I met Sir Jeremy at the UN or back in the Foreign Office where I was a Minister he never raised en eyebrow by a millimetre about the prospect of invading Iraq and lining up behind George W Bush. This is the puzzle that Chilcott failed to answer or even properly examine. Why did the state apparatus fail to persuade the prime minister or mobilise by other ways to stay Britain’s hand?
It would have made no difference to the invasion as the United States had no need of  the British military with its gung ho Colonel Tim Collins type warrior rhetoric. It would have been difficult for Tony Blair politically as the Conservatives in opposition were eager-beaver to prove they were the party of American neo-conservatism but there was no strategic advantage to the United Kingdom to be involved in the destruction of a Muslim state of 35 million people under a cruel dictator who sat on a Shia-Sunni-Kurd time-bomb.
Three times this century the deep British state represented by its full-time state functionaries failed to stand up to a prime minister and steer him away from major strategic errors.
The first was Iraq. Unlike Suez when top diplomats wore black ties to show disgust at Anthony Eden’s folly, no-one in Whitehall other than a Foreign Office lawyer resigned or protested.
The second error was the destruction of the state in Libya when David Cameron tucked in behind an over-excited Nicolas Sarkozy who was told late at night by the French intellectual Bernard Henri-Levy that he had a historic moment to get rid of Gaddafi and bring democracy to Libya which would be eternally grateful to France as a result.
Instead, the Sarkozy-Cameron intervention opened a 1700 kilometre breach in the southern Mediterranean security wall through which endless jihadis, economic migrants and refugees have fled from the warlords of Libya.
Every mistake made in Iraq was repeated in Libya, yet there is no evidence of any high official saying to David Cameron it would be a disaster even though the same officials have all been in post, in more subaltern positions than during the Iraq catastrophe.
The third foreign policy sinkhole where the state apparatus failed to protect a prime minister was Brexit. When David Cameron returned to power in May 2015, the high state apparatus should have come to him with a comprehensive plan on how to win the referendum.
Instead nearly a year was wasted in which Cameron continued to sneer at and denigrate the European Union. The Conservative Party conference in October 2015 was a festival of Ukip-style language against Europe with Theresa May declaiming that the number of Europeans in to the UK was “unsustainable”. This brought Tory party activists to their feet in delirium and set the tone for the entire Leave campaign.
As all the instant histories confirm, Cameron frittered away months on pointless negotiations with Brussels instead of reaching out to businesses and all voters to explain why a Brexit vote was wrong. The state apparatus was horrified at the thought of Britain amputating itself from Europe and embracing Ukip style isolationism. But why did they do nothing to guide Cameron in 2015 and the beginning of 2016 to work on obtaining a victory to prevent Brexit and save the humiliation of the prime minister being booted into history’s dustbin?
History will attach the failures in Iraq, Libya and on Brexit to the names of Tony Blair and David Cameron. And they have to accept ultimate responsibility. But the puzzle remains. Why did the Sir Jeremies of Britain’s deep state – Greenstock, Heywood and the rest – fail to coax the prime minister to more intelligent positions?
Denis MacShane was a PPS and Minister at the FCO 1997-2005. He is author of Brexit: How Britain left Europe (IB Tauris).
