'Political prosecutions'

In addition to Wong, Law and Chow, multiple other Umbrella activists are facing prosecution, including Benny Tai, a Hong Kong University professor who first suggested the 2014 protests.

"Never in Hong Kong's history have so many opposition politicians and activists faced court proceedings against them," according to Kong Tsung-gan, author of "Umbrella: A Political Tale from Hong Kong."

The Hong Kong government has consistently denied accusations that cases have been brought for political purposes.

"He didn't have to ask for a review of the original (community service) sentences," Patten said, adding that doing so risked undermining Hong Kong's reputation as "an international hub for the rule of law."

His and other jailed protesters' faces were a frequent sight on banners and leaflets at Sunday's march. Protester Danny Chan said older Hong Kongers like him "need to speak out, to support the young people in jail."

Limits on speech

This week lawmaker Cheng Chung-tai was found guilty of "desecrating" the standards of China and Hong Kong and fined $640 after he flipped over some plastic flags brought into the city's parliament by pro-Beijing legislators during a session last year.

A law recently passed by China's National People's Congress will also criminalize insulting the country's anthem, "March of the Volunteers."

While it is unclear how the law will apply in practice to the city, which has greater freedom of speech protections than China, the national anthem has been a key point of protest in Hong Kong, with local soccer fans repeatedly booing it during matches with China.

"Using laws to mandate 'patriotism' curbs the freedom of expression and reflects an increased degree of authoritarianism in Hong Kong," said Jeffery Ngo, chief researcher for Demosisto, Wong and Law's political party.

Increasing support, particularly among young Hong Kongers, for "localist" parties which advocate greater autonomy or even independence from China has also sparked a fiery response from Beijing.

Uncertain future

Translating political energy into concrete gains has proven difficult for Hong Kong's opposition, said Lev Nachman, an expert on Asian social movements at the University of California, Irvine.

He compared the Umbrella Movement to Taiwan's Sunflower Revolution, which occurred around the same time, a key difference being that supporters of the latter are now largely in power on the island, while a raft of Hong Kong protest leaders elected to office were swiftly removed.

"Although it was a great victory for Hong Kong activists to have them elected, the disqualification is a large setback," Nachman said.

Demosisto researcher Ngo said there were more avenues for the opposition to explore, "not least including the elevation of our democracy endeavor to the international level."

While both the UK and US have expressed concern over the situation in Hong Kong, former governor Patten was skeptical whether countries would risk economic ties with China over it: "I can't pretend that the rest of the world is going to be more heroic than is likely to be the case."

Speaking at Sunday's march, Ng said the opposition camp is facing a "difficult" task, "but when has it ever been easy to fight against authoritarianism?"

Next fight

Duncan Innes-Ker, Asia regional director for the Economist Intelligence Unit, said the traditional pro-democracy movement "has been undermined by a growing perception that there is no chance of persuading the mainland authorities to allow real democratic reforms."

A major test will come early next year, as by-elections are held to replace the disqualified lawmakers.

"If Hong Kong activists were able to mobilize and elect six localist officials in 2016, there is a chance they can do it again in the next election," Nachman said.

Ng was hopeful that there would be a record turnout for those elections -- as there was for votes last year -- but wary that many protest leaders would be blocked from standing for office, as multiple pro-independence candidates were in the past.

Innes-Ker warned that too many setbacks to the opposition could actually backfire on the government, leading to more radical tactics and greater disruption. "The danger will escalate if (the local government) fails to make progress in addressing the livelihood issues that represent the key cause of public discontent in the territory," he said.