Dominic Cummings has claimed that China breached high level systems to obtain “vast amounts” of classified Government information for years.

Boris Johnson’s former adviser said he and the then-Prime Minister were told about the breach in 2020 and that it involved so-called Strap material, a Government classification for highly sensitive intelligence material.

He said that fundamental infrastructure for transferring sensitive data around the British state was compromised “for years”.

Mr Cummings did not say how the system had been breached but that he would be willing to share what he knew with MPs if they were to hold an inquiry.

He told The Times: “What I’m saying is that some Strap stuff was compromised and vast amounts of data classified as extremely secret and extremely dangerous for any foreign entity to control was compromised.

“Material from intelligence services. Material from the National Security Secretariat in the Cabinet Office. Things the Government has to keep secret. If they’re not secret, then there are very, very serious implications for it.”

A Cabinet Office spokesman said: “It is untrue to claim that the systems we use to transfer the most sensitive Government information have been compromised.”

One former Whitehall official told The Telegraph Mr Cummings’s characterisation of what happened was “utter nonsense” but agreed that security breaches had occurred.

The source did not deny that Mr Johnson commissioned a report from Lord Sedwill, his cabinet secretary and national security adviser, on how the Chinese had been able to buy a company that controlled a data hub used by Whitehall.

In the background of this, two men alleged to have spied for China were accused of giving politically sensitive information to a Chinese intelligence agent over the course of around a year.

Former parliamentary researcher Christopher Cash and his friend Christopher Berry both denied passing secrets to China before the case was dropped by the Crown Prosecution Service (CPS) in September.

The case against the pair had alleged that information about the inner workings of the British political system and the Government’s position on Chinese businesses were passed to the agent, which was then handed to a senior member of the Chinese Communist Party and a Politburo member.

LATEST DEVELOPMENTS

• Keir Starmer publishes 18 pages of China spy case evidence
• Keir Starmer finally caves to pressure as PM vows to come clean on China spy scandal
• White House issues stark warning to Britain amid China spy scandal

Deputy national security adviser Matt Collins, whose witness statements were published on Wednesday, said sensitive information relating to the personal and political activities of MPs was also allegedly passed between the two men.

These included Jeremy Hunt being likely to pull out of the Conservative Party leadership race and Tom Tugendhat being “almost certain” to get a cabinet position from then-prime minister Rishi Sunak in exchange for support on foreign policy matters.

Mr Collins said a meeting between Mr Berry and a senior Chinese Communist Party (CCP) leader in July 2022 was “highly unlikely” to have happened “unless the Chinese state considered him to be someone who could obtain valuable information.”

At the time of his arrest, Mr Cash was director at the China Research Group (CRG), a group set up to formulate ideas on how to respond to the country’s rise.

Mr Collins said Mr Cash was made aware “in detail” of the July 2022 meeting, with the researcher allegedly sending Mr Berry a message which read: “You’re in spy territory now.”

The CPS’s case was that Mr Cash and Mr Berry became friends from as early as August 2017 when they were both teaching in the Hangzhou area of China.

During the time period the pair were alleged to have been spying, Mr Berry and the Chinese intelligence agent were based in China and Mr Cash was based in the UK.

The CPS alleged the intelligence agent commissioned at least 34 reports from Mr Berry, which included information obtained from Mr Cash following the agent’s requests for reports on specific topics.

Prosecutors alleged Mr Cash eventually began to share unsolicited “off-the-record” information, but most of the information from him was solicited by Mr Berry.

Mr Collins provided witness statements to the CPS, in which he called China “the biggest state-based threat to the UK’s economic security.”

The deputy national security adviser said “by its very nature”, the alleged sharing of information between Mr Berry, Mr Cash and the intelligence agent was “prejudicial to the safety or interests of the UK”.

He added that Mr Cash’s alleged involvement would have provided the intelligence agent access to the CRG, the parliamentary estate and at least two senior MPs, the then-chair of the foreign affairs select committee Alicia Kearns and her predecessor Mr Tugendhat.