The younger sister of a former leader of the now-disbanded Confederation of Trade Unions (CTU) has been remanded in custody after pleading guilty to perverting the course of justice on Thursday.

Marilyn Tang admitted to the West Kowloon Court that she went to her sister Elizabeth’s flat in Mei Foo after learning of her arrest by national security police for suspected collusion with foreign forces in March this year.

The court was told that on March 9, she went to the flat twice before officers arrived to seize evidence.

Police arrested her two days later and found a mobile phone and laptop that belonged to her sister. The devices contained family photos and letters that Elizabeth wrote to her husband, jailed former lawmaker Lee Cheuk-yan.

Elizabeth Tang is a former chief executive of the CTU.

In mitigation, the defence said the 63-year-old defendant, who obtained a master's degree in social work in 1987, had served the community her whole life, adding that the devices seized only contained personal information.

However, magistrate Patrick Tsang said imprisonment is inevitable, as her two visits to the flat showed that she had made a conscious decision to do so.

Marilyn Tang will be sentenced on December 21.