Even the confidences of marriage are, as Margaret Cook has displayed, now breached for political and personal ends.Most crucial of all, the political marriage of competence, trust and secrecy has been broken for ever. People no longer believe that the way we are governed works, and they have lost faith in their politicians. The conventions of secrecy have been replaced by a premium on candour. Yet the social conditions and political realities that made the regime possible in Victorian Britain do not obtain any longer The public is better educated and less deferential.

Governments of every colour have found the combination of flexible powers and equally flexible secrecy a persuasive argument against reform. It was only when the “mechanicals” began leaking information that the state came to pass secrecy laws. Though these acts – the most infamous of which was Asquith’s 1911 Official Secrets Act – were presented as defences against foreign enemies, their real purpose was to silence enemies within the state.The longevity of the gentlemen’s regime has been remarkable. Official secrecy was designed to control, in its own interests, the teeming mass of information at the state’s disposal. Senior politicians and officials had licence to spill the beans when they chose, but not the lower orders.

Its ideological key was the decision to give the new meritocratic civil service of the 1850s an ethos akin to that of the displaced aristocratic placemen. The standards of the new “regime of cram” were personified in the figure of the gentleman, who would combine the virtues of trust and competence with discreet respect for the confidences of his calling.This “honourable secrecy” did not amount to an oath of silence. He rarely strays away from the conduct and culture of the state, and especially the British civil service. But he finds time, for example, to celebrate Baroness Thatcher as a pioneer of openness (in local government), to dissect the collision of private and public worlds in the trial of Oscar Wilde, to describe Marie Stopes’s rage over the concealment of information about birth control, and to mock the Victorian Home Office’s opening of letters to stop foreign porn defiling public schoolboys; and he refrains from condemning Asquith’s leaks of critical information about the 1914-18 war in love letters to a young woman – even though the disclosures could have led to thousands of deaths.What emerges is the astonishing continuity of state practice. Government that denied the public full knowledge of BSE, that withheld the rules that regulate ministers’ behaviour until the Nineties and that censors the media through secret D-notices, is to be mocked and condemned.But it helps to understand, and Vincent’s account is enjoyable and illuminating. Secrecy is integral to any regime, but it has been utterly fundamental in Britain.