“We are looking at a more intelligence-led, investigative approach to leaking,” Sir Mark Sedwill, the cabinet secretary, told MPs last December after a torrent of Brexit-related leaks from cabinet meetings.

He continued: “Rather than simply treating it incident by incident. I hope we will have a chilling effect … A more intelligence-led assessment approach to identifying patterns, timings, etc, to enable us to have a better chance of identifying the prolific culprits.”

Sedwill told the Public Administration Select Committee he was “deeply concerned” by these leaks, saying they undermined the vital principles of collective responsibility: candour, confidentiality and commitment. Surprisingly, he revealed that Theresa May had never asked him to launch a leak inquiry, though said he had done so on his own account.

Sedwill’s new approach has not exactly proved a roaring success. He is in the thick of it after this week’s spectacular leak of the National Security Council’s decision to allow the Chinese telecoms giant Huawei to provide non-core parts of the UK’s 5G mobile phone network. The group, chaired by May and comprised of cabinet ministers, intelligence and security chiefs, is the most sensitive inner sanctum in the government machine. On the Richter scale of leaks, the revelation to The Daily Telegraph is an 11.

Inevitably, ministers have queued up to deny responsibility. Initially, one reportedly tried to point the finger of suspicion at civil servants, which naturally went down very badly with officials.

Sedwill’s pledge to crack down on leaks seems to owe more to Inspector Clouseau than Hercule Poirot. You don’t have to be George Smiley to deduce that the most likely leaker was a cabinet minister who wants to succeed May (which reduces the list of suspects to 28). Or work out that the motive was to play to the gallery of Tory MPs and members by appearing to take a tough stance against China.

The Telegraph story said May approved Huawei’s role despite warnings that it posed a risk to national security by Sajid Javid, Jeremy Hunt, Gavin Williamson, Liam Fox and Penny Mordaunt. They have all denied involvement in the disclosure.

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The leak provides the most graphic example to date of our dysfunctional government. Even before it happened, the Tory chief whip Julian Smith told the BBC that Brexit had created “the worst example of ill-discipline in cabinet in British political history”.

Well, it just got even worse.

May has contributed to the turmoil by promising Tory MPs she will stand down if they pass her Brexit agreement. They are now agitating for her to quit even if her deal is not approved. She won only a temporary reprieve this week; the demands will return after the poor Tory results expected in next month’s local authority and European parliament elections.

The Telegraph, of course, was doing its job and disclosing a matter of public interest. It should not be pilloried or pressurised during Sedwill’s inquiry. It did not publish any sensitive material. The government’s decision would have been announced in due course. It would rather have done so on its own terms, and certainly not before the chancellor Philip Hammond tried to win UK contracts at the major conference now taking place in Beijing on China’s Belt and Road initiative.

The leak allowed some MPs to claim ministers are putting the need for post-Brexit trade deals before national security, as the United States and other “five eyes” allies like Australia are very wary of Huawei’s close links with the Chinese government. The leak will damage the UK’s reputation in their eyes – another embarrassment for May, who, ironically, must be the most cautious politician in the world when it comes to the media.

Although the leak potentially involves a breach of the Official Secrets Act and could result in a prosecution, no one at Westminster is placing bets on someone being caught, even if the police or spooks are drafted in to help Inspector Sedwill.

Having worked as a Westminster journalist since 1982, I can imagine that combing through phone or email records will produce nothing. Information is often relayed through intermediaries such as the special advisers to ministers. Or a fleeting face-to-face chat between a minister and journalist, sometimes in a chance meeting. Tracks are covered; proof is hard.

Leakers rarely get caught, especially when the trail leads to a politician or something that would embarrass the Whitehall machine. I recall that a journalist who posed as a Cabinet Office secretary and leaked a pile of confidential documents was never prosecuted.

It will be interesting to see if there’s an exception to the rule on this occasion. I don’t doubt Sedwill’s determination to get to the bottom of it. But I do doubt that he will.