Hong Kong's last British colonial governor Chris Patten attacked the city's pro-independence movement Friday as the push for a split with China grows over fears of Beijing's tightening grip.

Patten said he was fully behind the strengthening of democracy in Hong Kong, but accused independence activists of "making a mockery" of the issue.

His comments came on the same day that two publicly elected young lawmakers, Baggio Leung and Yau Wai-ching, appealed against a ban against them taking up their seats in the legislature.

They were disqualified in a High Court judgement last week after they added expletives and used derogatory terms for China when taking their oaths of office in October.

The High Court's move had been preempted by an an earlier intervention from Beijing which said they should not be allowed to join parliament.

Patten was governor of Hong Kong when it was handed back to China by Britain in 1997 under a semi-autonomous deal protecting its freedoms for 50 years. There are deep-seated concerns that those liberties are now under threat.

He said that he believed passionately in the city's rule of law and freedoms, but dismissed the pro-independence camp as resorting to headline-grabbing "antics".

"It would be dishonest, dishonourable and reckless for somebody like me to pretend that the case for democracy should be mixed up with an argument about the independence of Hong Kong," he told a packed room at the Foreign Correspondents' Club during a visit to the city.

Patten said independence would never happen and that the movement had diluted support for democracy.

"Taking oaths isn't something of a lark," he added,

"In London, I take an oath with my hand on the bible," Patten said.

- 'Moral high ground' -

Pro-democracy campaigners who led mass rallies calling for fully free leadership elections in 2014 risked losing the moral high ground by championing independence and self-determination, Patten said.

Some of those leaders, including popular figures Joshua Wong and Nathan Law -- Hong Kong's youngest lawmaker -- are now campaigning for self-determination, with independence as an option, after the huge "Umbrella Movement" protests failed to win concessions on political reform.

Patten told AFP that they should instead campaign for "immediate objectives" such as reform of the pro-Beijing committee that currently chooses the city's leader and better democratic representation in the legislature.

"There are lots of people who agreed with them on democracy who won't touch this stuff about self-determination with a barge pole," he told AFP.

However, Patten did criticise the slow pace of democratic development in Hong Kong -- something which has frustrated young campaigners -- and said the city should eventually be able to choose its own leader.

The city's next chief executive will be chosen in March 2017 by an electoral committee of interest groups skewed towards Beijing.

Patten also told the audience during his FCC address that Beijing should leave the Hong Kong courts to decide on the fate of the banned pro-independence legislators.

Responding to Patten's comments, disqualified lawmaker Leung said those elected on a pro-independence ticket could not ignore the calls of voters.

"The discussion of self-determination or even independence is a step...to protect the freedom of our system," he told reporters at the High Court.