Cabinet Secretary Sir Mark Sedwill has reportedly demanded that ministers, who attended the secret talks about whether to grant Chinese telecoms giant the go-ahead to participate in the UK’s 5G communications network, confess or deny if they were behind the leak.
:: What ministers who were there are saying
Sky News political editor Beth Rigby has been told the inquiry could turn into a criminal investigation involving the police.
Such an escalation would significantly raise the stakes as detectives have the power to interview suspects under caution and bring charges under the Official Secrets Act.
The decision of whether to prosecute someone under the legislation lies with the attorney general and anyone found guilty of the unauthorised disclosure of information faces up to two years in prison or an unlimited fine, or both.
The Metropolitan Police could neither confirm nor deny any investigation had been requested or was under way.
The leak of the discussions from the National Security Council (NSC) – where senior ministers are briefed by intelligence chiefs from MI5, MI6 and GCHQ – has prompted an outcry at Westminster, where it was linked to manoeuvres around the Tory leadership contest.
There are also concerns it could harm intelligence-sharing relations with key allies.
The details were revealed in The Daily Telegraph on Wednesday, along with a list of cabinet ministers who raised concerns about the idea.
Defence Secretary Gavin Williamson and Foreign Secretary Jeremy Hunt have publicly denied that they were responsible.
Home Secretary Sajid Javid has also said it was “completely unacceptable” for any minister to “share sensitive information that cannot be out in the public domain”.
Sources close to International Trade Secretary Liam Fox and International Development Secretary Penny Mordaunt have also denied they were involved.
Chancellor Philip Hammond, who is attending a top-level conference in Beijing, said serving on the NSC was “a great privilege”.
He said: “To my knowledge there has never been a leak from a National Security Council meeting before.
“Therefore I think it is very important that we get to the bottom of what happened here.
“It’s not about the substance of what was apparently leaked – it’s not earth shattering information – but it is important that we protect the principle that nothing that goes on in National Security Council meetings must ever be repeated outside the room.”
The NSC meeting on Tuesday saw Huawei granted restricted access to build “non-core” infrastructure such as antennas, Whitehall sources confirmed.
But the firm will be blocked from involvement in the most sensitive areas of the network.
Other members of the Five Eyes intelligence-sharing group, which includes the US, Canada, Australia and New Zealand, have already raised concerns.
The US and Australia have barred Huawei from supplying key elements of their infrastructure, while New Zealand and Canada are still considering the matter.
Huawei denies having ties to the Chinese government.
But with a legal obligation to cooperate with the state’s intelligence agencies, critics worry that no Chinese company can ever be truly independent.
There are also concerns that the Chinese government could require the firm to install technological “back doors” to enable it spy on or disable Britain’s communications network.
Decisions of the NSC are taken collectively, but it was reported that concerns were raised during Tuesday’s meeting by a number of ministers.
They included Mr Javid, Mr Hunt, Mr Williamson, International Trade Secretary Liam Fox and International Development Secretary Penny Mordaunt.