No popular impression is more precious to those who govern than the impression on the part of the governed that more is known than can be divulged.
William Whitelaw understood this better than most. When I was a callow young Tory MP in the 1980s, and he was home secretary, I was briefly caught up in a flutter of backbench concern about telephone-tapping. More of this, it seemed, was going on than had been supposed, and the means of democratic oversight did not seem to exist. A small group of us on the government benches, all backbenchers, asked if we could talk to Willie about the problem. Alongside my friends, and not without trepidation, I entered the great man's Commons office.
The home secretary roared his welcome and, spurning his big desk, gestured us into comfortable armchairs. Out came a whisky bottle and tumblers, and what seemed like half pints of the stuff were dispatched; there was no saying no. 'Now,' said Willie, 'tell me.'
The leader of our group began to tell him, but within a minute was chummily interrupted. Good Heavens, rumbled Willie, we had not - had we? - thought for a moment that our concerns were not understood, were not his concerns, or that our instincts in this matter were not four-square with his own? If we had been troubled, he had been troubled too, and now he was doubly troubled that we were troubled. But....
And here the home secretary put down his whisky glass and leaned confidingly towards us. There were things he knew about the Threat. Things he had to know. Things he knew that if we knew too, then we would know why he was where he was and did what he had to do.
We stared at him, agog. He rumbled on. He told us how acutely sensitive he - of all people - was to any threat to personal liberty; how important he - of all people -knew it to be that those Right at the Top in government kept tabs on what the police and the security services were doing. And he did keep tabs. Oh yes. But it was in the nature of a home secretary's job that information came his way which was of the last importance but which he could not share. It pained him that he could not share it with excellent fellows like us.
He trusted us, of course, he said - implicitly. He well knew that not a word that passed between us within those four walls would be repeated. But he did not -could not; we knew why - trust every colleague in quite the same way, and once home secretaries began confiding secret intelligence to members of parliament, where would it end - where indeed?
Could he then, he concluded, ask us to trust him? Could he ask us to accept that he would not do whatever it was he did without very good reason? He felt a brute asking us to rely on him like that, to follow him in the dark, as it were, but he dared hope we knew we could. Our glasses were recharged generously.
I left a little tipsily, feeling that a great confidence had been reposed in me. From now on I would help keep Willie's secrets.
I thought of Lord Whitelaw last week as the media electric storm rolled and echoed around the discovery, the week before, that No. 10's dossier on the deadly secrets of Saddam Hussein had been culled by someone working for Alastair Campbell from an old PhD thesis and the back-number of a defence magazine. I was on the Tube on Friday sitting opposite a couple of friends - one youngish and in a suit, the other younger and casually dressed - discussing that dossier. 'Apparently,' said the first, 'they got it off the Internet from a 14-year-old kid who'd written it for his GCSE.'
'Yes,' (with authority), 'fourteen'.
I don't believe in turning-points, but if I did, then the dossier would be D-day candidate for the moment when No. 10's propaganda war on Iraq went into irreversible retreat. It was a huge mistake to attempt the dossier, any dossier, in the first place. In my view Colin Powell made a similar error in his presentation at the United Nations of evidence for Iraqi evasion. Unless you've a real stonker of a revelation to disclose, it is always an error to show people your hand after having raised expectations as to what it might contain. The higher the expectations, the more closely the hand should remain concealed. A dossier should knock you down, or it should never have been brandished.
Most people are like me: suckers for the 'trust me: I know things I cannot reveal' avoidance technique. I feel an instinctive respect for those who cannot state their reasons. I doubt (I always doubt) but I am ready to give the benefit of the doubt. Asking someone to trust you is, after all, a kind of compliment. But when I am invited to see evidence so far withheld, I naturally suppose I shall be offered a taste of the best they've got.
If that then disappoints - and because I assumed it would be the best they have - I am doubly dismayed. If that's the best they can do, I say to myself, then what's the rest like? If a cribbed PhD thesis was the best Downing Street could do when rising to the challenge of providing Her Majesty's Government's evidence of the Iraqi threat, and if the American secretary of state was prepared to praise it without looking at it (or, worse, praise it after having looked at it), then what's the rest like? What level of assessment can the Prime Minister bring to intelligence reports from abroad if he is prepared to sign off without scrutiny his own staff's drafts? Plainly the man is easy to impress.
Too many people now central to the workings of British government and administration have a professional background and stake in what is called Communications. If from the start of this Iraq crisis our government had communicated absolutely nothing of what they knew about Saddam, but instead asked us to trust them, then the British people would be more convinced than is now the case that our masters have their reasons. If Disraeli ever really did say, 'Never apologise. Never explain,' he was right.
Matthew Parris is a political columnist of the Times.