Former media tycoon Jimmy Lai committed offences of "a grave nature" and his role as "the mastermind and the driving force" behind conspiracies to seek foreign sanctions warranted a tougher sentence, three High Court judges ruled on Monday as they handed down a 20-year jail term.

The 78-year-old, who founded the now-defunct Apple Daily newspaper, was convicted in December last year by judges Esther Toh, Susana D’Alamada Remedios and Alex Lee of two courts of conspiracy to collude with foreign forces and a third charge of conspiracy to print seditious material.

The collusion offence under the National Security Law has a two-tier sentencing mechanism, and anyone found guilty of committing an offence of "a grave nature" faces a term of 10 years to life imprisonment.

The bench ruled that the conspiracies in this case fell "within the category of offences of a grave nature", as the crimes that "were clearly premeditated" took place at a time "when Hong Kong had hardly recovered from the social turmoil" in 2019.

Sanctions, blockade or other hostile activities "were in fact taken by foreign countries" against central and local authorities, according to the judges.

"Such adverse measures have not been removed even up to today," they said.

"Although it was not the case that the conspiracies were the only cause of the [sanctions, blockade, or other hostile activities], it is wholly unrealistic to say that the defendants’ activities were not a contributing cause."

While adopting 15 years' imprisonment as the starting point for each of the national security charges, the judges said Lai warranted heavier penalties as he was found to be "the mastermind and the driving force behind these conspiracies".

But they also took into consideration the defendant’s mitigation and accepted that "Lai’s old age, health condition and solitary confinement would cause his prison life to be more burdensome than that of other inmates".

Eighteen of the 20 years would be served consecutively to Lai's separate sentence of five years and nine months for fraud.

"The court bore in mind that the offence was of a totally different nature to the present offences, also unrelated to the present case," the judges said.

The court also ruled that the conspiracies "could not have been carried out without the full cooperation" of the three corporate defendants, namely Apple Daily Limited, Apple Daily Printing Limited and AD Internet Limited.

The judges said they were "unable to see any cogent mitigation factors" and fined each of the firms HK$3,004,500.