Prime Minister Theresa May on Wednesday sacked Gavin Williamson as defence secretary over the leak last month of the bitterly-disputed decision made at the April 23 meeting of the National Security Council (NSC).

Following the police announcement, Williamson, who has strenuously protested his innocence, said he was the victim of a shabby "witch-hunt".

He hit out at May and Mark Sedwill, Britain's top civil servant who carried out the government's internal leak inquiry that led to his sacking.

Williamson said in a statement: "With the Metropolitan Police not willing to do a criminal investigation it is clear a proper, full and impartial investigation needs to be conducted on this shabby and discredited witch-hunt that has been so badly mishandled by both the prime minister and Mark Sedwill."

NSC discussions are only attended by senior ministers and security officials who first sign the Official Secrets Act that commits them to keep information private or risk prosecution.

Some senior opposition figures called for a police investigation.

But in a statement on Saturday, Assistant Commissioner Neil Basu, the head of Specialist Operations at London's Metropolitan Police, said a probe would be inappropriate.

"I am satisfied that what was disclosed did not contain information that would breach the Official Secrets Act," said Basu, whose section is responsible for investigating alleged criminal breaches of the act.

"I am satisfied that the disclosure did not amount to a criminal offence, either under the Official Secrets Act or misconduct in a public office. No crime has been committed and this is not a matter for the police.

"The leak did not cause damage to the public interest at a level at which it would be necessary to engage misconduct in a public office.

"It would be inappropriate to carry out a police investigation in these circumstances."

The leak, which appeared in The Daily Telegraph newspaper, suggested May had cleared Huawei to be involved in "non-core" elements of the 5G network, such as antennae.

Williamson told Saturday's Daily Mail newspaper: "I have been royally screwed over. It is pretty painful. The only thing I want to do now is clear my name." Newspapers speculated Saturday that Williamson, a sharp operator, was plotting his revenge on May.

The 42-year-old was a trusted ally of the prime minister.

He was May's parliamentary campaign manager when she successfully ran to become Conservative Party leader in 2016.

Williamson was duly rewarded with the job of chief whip -- tasked with enforcing discipline for the Conservatives in parliament and wielding power over misbehavers.

The Times quoted one ally as saying: "Gavin knows where the bodies are buried -- because he buried them himself." He was replaced as defence secretary by Penny Mordaunt.

The US is adamantly opposed to Chinese tech giant Huawei's involvement in developing Britain's 5G network due to the firm's obligation under Chinese law to help its home government gather intelligence or provide other security services when required.

David Lidington, May's effective deputy, said Thursday there were no plans to pass information from the internal leak inquiry to the police, saying the prime minister regarded the matter as closed.

Basu said that unless a crime was alleged there was nothing for the police to investigate and his unit had not been provided with any evidence of an alleged crime.