The man, aged in his 20s, was arrested under the Official Secrets Act in March 2023 after allegedly passing top secret documents to China.

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The parliamentary aide, who has not been named, previously released a statement through his lawyers claiming he is innocent.

He was arrested in Edinburgh on March 13 last year, while a second man, in his 30s, was detained in Oxfordshire, according to cops.

Searches were also carried out at an east London property.

In an update from Scotland Yard, a spokesman said: “Officers have been in liaison with [the] CPS in relation to this investigation and a case file has now been passed to them for consideration.

“Both men remain on police bail at this time and inquiries continue.”

Once the police consider that they have enough evidence when investigating they will pass the case to the CPS.

The CPS will then review the evidence and consider whether they can bring a prosecution.

If the police don’t think they have enough evidence they would not pass the case to the CPS and no further action will be taken against the suspect.

The researcher has previously lived and worked in China and has been working with parliamentarians for a number of years.

He is understood to have links to senior Conservative MPs who have access to highly sensitive or classified material.

The suspected spy was handed an access-all-areas pass at Westminster after lobbying for ­Foreign Affairs Committee chair Alicia Kearns to get elected.

He also had links with security minister Tom Tugendhat.

At the time, he was working as a researcher for the China Research Group of MPs, which was set up by Mr Tugendhat and run by Ms Kearns.

Insiders previously said the arrest is likely to be the “tip of the iceberg” and a spy ring could be operating in Westminster.

In his role with MPs, the man may have had access to “highly sensitive” documents as well as private briefings from ministers, senior officials, and dissidents critical of China’s ruling Communist Party.

While other experts claimed the arrest should be a “wake up call” for Britain.

In a previous statement released through his lawyers, Birnberg Peirce, the accused man said: “I feel forced to respond to the media accusations that I am a ‘Chinese spy’.

“It is wrong that I should be obliged to make any form of public comment on the misreporting that has taken place.

“However, given what has been reported, it is vital that it is known that I am completely innocent. I have spent my career to date trying to educate others about the challenge and threats presented by the Chinese Communist Party.

“To do what has been claimed against me in extravagant news reporting would be against everything I stand for.”

Birnberg Peirce are one of Britain’s leading human rights law firms whose clients have included Julian Assange, the Wikileaks founder, and Shamima Begum, the east London schoolgirl who joined Islamic State.