Meanwhile, one key question for the camp as a whole is whether the Alliance for True Democracy, which brings together 26 of the 27 pan-democratic lawmakers, can hold together.

The question arises after League of Social Democrats and People Power lawmakers urged their supporters to vote against the alliance's reform plan on Tuesday. The plan, under which the public, political parties and a nominating committee could all choose candidates, finished third in the voting and will be an option in the referendum.

Alliance convenor Professor Joseph Cheng Yu-shek said the two parties had since agreed to campaign for its plan in the referendum, despite the fact a proposal from People Power will also be on the ballot. A plan by Scholarism and the Federation of Students topped Tuesday's poll.

"We agree there is room for improvement in terms of … mutual trust," Cheng said. "But all member groups have agreed to … push for the alliance's proposal to win."

But the Democratic Party, which does not see public nomination as indispensable, expressed disappointment at the behaviour of the two groups. Lawmaker Sin Chung-kai said: "The party will discuss the prospect of staying in the alliance."

Another moderate pan-democrat, who declined to be named, went further, declaring that Tuesday's events marked a formal split in the camp. The alliance was now irrelevant - and next month's vote might be too.

"Middle-ground voters may choose not to cast ballots … because all three proposals call for public nomination" the pan-democrat said. "Radicals can't claim the referendum results represent the views of the majority of Hong Kong people if fewer than 200,000 people turned out."

By comparison, some 222,990 Hongkongers cast ballots in a mock chief executive election in March 2012 organised by the University of Hong Kong's public opinion programme.

A so-called de facto referendum in 2010 is also credited with encouraging Beijing to talk to the Democratic Party, eventually leading to a deal for a more democratic Legislative Council election in 2012.

A researcher affiliated with the central government, who spoke on condition of anonymity, said there could be room for discussion between pan-democrats and Beijing if the alliance's three-track plan won the vote.

"The alliance's proposal allows some flexibility for discussion between the two sides. It is a choice to be made by Hong Kong people," he said. "As the Hong Kong government is expected to present its reform proposal later this year, there is still time for dialogue between pan-democrats and the central government."

But Civic Party lawmaker Ronny Tong Ka-wah, who saw his moderate plan rejected on Tuesday, is pessimistic. He believes the vote will make it harder to find a reform package Beijing will agree to and that wins over the five or so pan-democrats it will need for a two-thirds majority in Legco. He also believes Occupy's plan to block streets in Central is now likely to go ahead.

"The Occupy Central movement has been hijacked by radicals and the civil disobedience is very likely to happen," he said. "It means the odds of failure to reach a consensus … are quite high."

POLL POSITIONS

Votes won by various political reform proposals during the Occupy Central movement's third deliberation day:

1,142 votes

708 votes

452 votes

76 votes

43 votes

17 votes

15 votes

8 votes