A group of high-profile Hong Kong pro-democracy activists including the media mogul Jimmy Lai have been sentenced to jail terms of up to 18 months for organising or attending “unauthorised assemblies” during mass protests that rocked the city in 2019.

In the latest blow to Hong Kong’s pro-democracy movement, Lai and the veteran activist Lee Cheuk Yan were each sentenced to 12 months in jail. Another activist, “Long Hair” Leung Kwok-hung, received the longest sentence, of 18 months, while Martin Lee, an 82-year-old barrister widely known as the father of Hong Kong democracy, and Margaret Ng, a 73-year-old barrister and former legislator, were given 11 and 12 months respectively, both sentences suspended for two years.

The jail terms were ordered in the first of two sentencing hearings on Friday – one relating to a protest on 18 August 2019 and another two weeks later on 31 August. Lai and Lee Cheuk-yan were defendants in both cases. Lai, who is facing other charges including under the national security law imposed by Beijing last year, has been detained on remand since late last year.

Separately, prosecutors laid a further national security charge against Lai on Friday, accusing him of conspiracy to collude with foreign forces, and another criminal charge of conspiracy to pervert the course of justice. Both reportedly relate to the case of Andy Li, an activist who was caught by Chinese authorities attempting to flee Hong Kong for Taiwan by boat.