Westminster is having one of its fits of indignation about anonymous sources. The present moral panic was triggered by a long message from Dominic Cummings, the prime minister’s chief of staff, to James Forsyth, political editor of The Spectator.

The message said, “The negotiations will probably end this week”, and blamed Leo Varadkar, the Irish prime minister. It said that if he rejected the latest proposal, and Boris Johnson won an election, the plan would be dead and Ireland would end up worse off with a no-deal Brexit.

Forsyth didn’t say it was Cummings, just that it was from “a contact in No 10”, but the unrestrained language and the length (800 words) made it as hard to identify the culprit as if we were looking at a toddler’s face covered in chocolate.

It seemed recklessly counterproductive, yet on Wednesday Varadkar and Johnson met in person in Cheshire and arrived at an unexpected preliminary agreement. It wasn’t clear whether Cummings’ message had helped or hindered this breakthrough, but it undoubtedly helped journalists to understand the thinking of the prime minister’s main adviser.

So what is the fuss about? I think it is mainly a reflex that assumes the government is manipulating the media by secret means, a belief that is as old as time. But as everyone assumed it was Cummings, this particular example wasn’t very secret.

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Some observers complain about comments being ascribed to “sources” rather than official spokespeople. In my view, this is a minor sharp practice in which the Labour Party engages as much as the government. Labour press officers sometimes ask to be quoted as “a source” rather than as someone speaking officially for the party or for Jeremy Corbyn. This means their bosses cannot be held to account for what they say.

Jill Rutter, a former civil servant, says that when government special advisers do this it allows them to avoid the rules about their conduct. There is a code for special advisers – political appointees who act as temporary civil servants – that says, among other things, that they are not allowed to engage in personal attacks, but if they are quoted as “sources”, no one knows if they’ve done it. Unless they are Cummings sending 800-word text messages to The Spectator.

Rutter’s concern is high-minded but unenforceable. People have always told journalists things anonymously. If we agree with the outcome, such as bringing Richard Nixon down over Watergate, it is all about protecting sources and investigative journalism and free speech. If we disagree with the outcome, such as Cummings winding up opponents of a no-deal Brexit by suggesting, anonymously, that the prime minister will not obey the law, it’s an outrageous abuse of power.

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All it is is news. If a source tells a journalist something that makes an interesting story, which would sell papers in the old days or drive web traffic now, we’ll publish it if we think it is true and not libellous. And if the source asks not to be identified, we will usually decide that it is better for the public to know than for the story not to be published at all.

Once upon a time, the relationship between politicians and Westminster journalists might have been too friendly, but the rules were changed. One of the biggest changes was when briefings by the prime minister’s official spokesperson were put on the record and published by the government – a change made by Alastair Campbell, when he worked for Tony Blair.

Yet he is remembered as an arch-practitioner of the dark arts of “spin”. And of course, he was sometimes an anonymous source. He has never quite admitted saying Gordon Brown had to get a grip on his “psychological flaws”, but everyone knew it was him then just as everyone knows what Cummings is up to now.