MI5 may have issued a rare alert notice about a lawyer who it claimed was acting on behalf of China’s ruling communist regime as a distraction from Partygate, a tribunal has heard.

The Security Service issued an interference alert against Christine Lee in 2022, warning MPs that she was a suspected Chinese agent who had engaged in “political interference activities” on behalf of a branch of the Chinese Communist Party (CCP).

The Investigatory Powers Tribunal in London heard that Barry Gardiner, the former Labour MP for Brent North, told Ms Lee that it had been suggested the alert had been issued to “detract attention” from then-Prime Minister Boris Johnson’s apology for the Partygate scandal the previous day.

Ms Lee donated more than £500,000 to Mr Gardiner, who was chairman of the now-disbanded Chinese In Britain All-Party Parliamentary Group on which she sat, which the Security Service said was provided by foreign nationals and “undertaken in covert co-ordination” with the CCP branch.

Ms Lee denies the allegations and is taking legal action against the Security Service with her son, Daniel Wilkes, who lost his job with Mr Gardiner following the alert, arguing that issuing the alert was unlawful and interfered with their human rights.

In a text, forwarded to Ms Lee by a friend, Mr Gardiner said: “Many people have said to me that they believe the reason for putting out the story when they did was to detract attention from Boris’ Partygate apology which was announced the day before at PMQs.

“I had never believed that the Security Services would be overtly party political in that way.

“What has also been suggested to me is that the Security Services may have wished to ‘pick a fight’ or to ‘detract attention’ from something else and that we were simply collateral damage.

“The fact that they have apparently failed to take any further action for the supposedly ‘illegal’ activity which they alleged had taken place, leaves me deeply sceptical.”

The alert about Ms Lee was issued on January 13 2022, a day after Mr Johnson apologised to the House of Commons for breaching Covid lockdown rules.

At the hearing on Monday, Ramby de Mello, representing Ms Lee and Mr Wilkes, said it was “plainly wrong” for the notice to have been issued.

He said: “Such a notice was unprecedented and as far as we are concerned it was the first time it was ever issued.

“The notice, alert notice, contains factual errors and is inaccurate and should not have been issued and was issued unlawfully.”

In written submissions, Mr de Mello said that Ms Lee engaged in activities including travelling to China and Hong Kong for business, meeting Chinese officials and making speeches that “criticised the protesters in Hong Kong for using violence”.

But he said that Ms Lee “did not know at the time, and had no reason to believe” that the activities “could fall foul of national security measures based on unacceptable business or political activities connected with China or UK MPs”.

The tribunal was told that the donations to Mr Gardiner came “overwhelmingly” from “profit costs” of her law firm and that the Security Service failed to consider that it was “unlikely” she would have been recruited as an agent due to her Christian beliefs.

Mr de Mello said the alert had “catastrophic” consequences, with Ms Lee receiving “sustained abuse, threats of death and rape” and remaining “most of the time in hiding”.

Mr Wilkes had his parliamentary security access revoked and lost his job with Mr Gardiner after the Security Service “spoke to” the former Brent North MP, who is now a candidate for the Brent West constituency.

Mr de Mello said that Mr Wilkes was given “an ultimatum: resign or be sacked” and “but for the Security Service’s act of branding Ms Lee a spy and their conversation with Mr Gardiner” he would not have lost his job.

Mr Wilkes is also seeking unspecified damages.

The Security Service is contesting the case, claiming that its decision was “rational and lawful”.

In written submissions, Victoria Wakefield KC, for the Security Service, said: “The decision to issue the interference alert was made in the discharge of the respondent’s statutory function to protect national security, in particular, its protection against threats from the activities of agents of foreign powers and from actions intended to undermine parliamentary democracy by political means.

“The respondent assessed that Ms Lee posed a risk of this nature, and its judgment was that the issuing of the interference alert was the most effective and proportionate means to address that risk. Those assessments were rational and lawful.”

The barrister continued that while it was accepted that the notice had a “significant effect” on Ms Lee, she was not “entitled to keep quiet” the nature of her “involvement in political interference activities” and she could have no “legitimate expectation of privacy” as a result.

She added: “In the present case, the respondent concluded on the information available to it that Ms Lee posed a threat to national security and that action was necessary to counter that threat.”

The hearing before Lord Justice Singh, Lord Boyd and Judge Rupert Jones is expected to conclude on Tuesday, with a judgment expected in writing at a later date.