ANOTHER day, another leak.

But there are leaks and there are leaks and the latest one from the “holy of holies”, the National Security Council, has sent shockwaves across Whitehall and Westminster.

We have, of course, become accustomed to ministers in Cabinet briefing about the latest twists and turns of the Brexit psychodrama; there have even been occasions when a titbit emerges even before Theresa May has wrapped up a meeting.

But now it seems someone, somewhere has become so brazen, indeed so irresponsible, that they feel they can start giving out information of a highly sensitive nature on security matters.

The granting of a contract to Huawei, the Chinese company, to supply equipment for the UK’s 5G mobile phone networks is controversial.

Several ministers at the NSC expressed concerns about security; Huawei operates under the governance of a Communist regime.

Indeed, the US has barred Huawei from involvement in official networks and has put pressure on its Five Eyes intelligence partners like Britain to do the same because of security concerns surrounding the company's links with the Chinese Government.

At the CyberUK conference in Glasgow, David Lidington, the PM’s de facto deputy, sought to allay fears, emphasising the Government would do nothing to compromise national security. He insisted UK ministers took the security of the country’s telecommunications networks extremely seriously and there were “rigorous and tested procedures” in place to manage any risks.

But the whys and wherefores of Huawei’s involvement in the UK’s digital future has been overshadowed by process on two fronts.

Firstly, apart from anything else, the leak undermines the very fabric of good government.

The NSC is meant to be a forum where senior ministers and security officials from the likes of MI5 and MI6 can discuss frankly highly sensitive material.

If any of them feel that what they say can end up on the front of a newspaper or at the top of a news bulletin, then they are going to think twice about offering honest opinion, which, in theory at least, could not only compromise the nation’s security but also cost lives.

Secondly, there is the political dimension. The suggestion is that the person who leaked the Huawei information was doing so to enhance their leadership credentials ie to be seen to be “tough on China”. Although without knowing who the leaker is, it is difficult to see how this could be of any benefit. Indeed, the phrase crass stupidity springs to mind.

Nonetheless, with such a claim hovering over Westminster senior Cabinet minister after senior Cabinet minister broke cover yesterday to decry the “utterly appalling” leak and insist: “It was not me, Guv.”

Sir Mark Sedwill, the Cabinet Secretary, who also wears another hat as the Government’s National Security Advisor, once he was peeled from the ceiling, launched a Whitehall probe; meeting the demand from across the Commons.

In a “strongly-worded” letter to all NSC members, he called for full co-operation from ministers and civil servants.

But it was not enough. Sir Michael Fallon, the former Defence Secretary, urged No 10 ie the PM to “wake up” to the seriousness of the leak and demanded Scotland Yard be called in.

Indeed, Lord Ricketts, the former National Security Advisor, suggested an almost Bondlike approach, suggesting investigators from the Security Service, MI5, could be brought in "to make the culprit feel very uncomfortable".

Of course over the years, there have been leak inquiries where top civil servants have sought to get to the bottom of an embarrassing revelation from deep inside Government. But none has ever produced a result; none has ever felt the culprit’s collar. Except, that is, for one.

In the run-up to the 2015 General Election, Alistair Carmichael, the then Scottish Secretary, held up his hand and admitted authorising the leaking of a civil service memo by his special advisor. He initially denied any knowledge, claiming the first he had heard of the leaked memo was when he received a phone-call from a reporter.

Frenchgate, as it was dubbed at the time, centred on a claim First Minister Nicola Sturgeon had, in private talks with the French ambassador, secretly admitted to preferring David Cameron to remain as Prime Minister rather than his Labour opponent Ed Miliband. It was, Mr Carmichael obviously believed, political dynamite. The only problem was it was completely untrue.

Later, the Orkney and Shetland MP said he "enormously" regretted his involvement in the leaking of the memo.

While the response to the NSC leak might for a while stem the steady flow of information from the inner sanctum of Whitehall into the public domain, the never-ending tunnel that is Brexit probably means normal service will resume fairly quickly.

With a Tory leadership contest on the horizon, Downing St’s plumbing is not going to be fixed any time soon.