Nevertheless, the government's proposed solution is causing even some allied lawmakers to baulk.

And according to Dr Ma Ngok, associate professor in the Chinese University's department of government and public administration, the plan would distort Hong Kong's party-list proportional representation system, which allocates seats in a constituency in accordance with the votes won by parties or lists of candidates.

'The distribution of seats in Legco would not reflect the will of the electorate at the time of the previous election under the government proposal,' he said.

To understand why, you have to look at the complicated system by which the Legislative Council fills its seats for geographical constituencies. Under the proportional representation system used since 1998, parties or non-affiliated groups rank candidates on lists. The chance of winning a seat is based on a 'quota' - obtained by dividing the number of valid votes cast in the constituency by the number of seats. If a party gets enough votes to meet the quota, it automatically wins a seat. Who gets the remaining seats will be determined by ranking the so-called remainder votes. When several candidates run on the same list, those ranked low on the slate can miss out because the party's remainder voters aren't enough to win another seat.

The government proposal would change the way Legco fills a vacancy arising from a legislator's resignation, death or incapacitation. Instead of holding a by-election to fill the seat, as is now the case, the post would go to the highest-ranked candidate not elected on whichever list had the most remainder votes at the previous election.

Take this example: in the 2008 Legco election, 236,244 votes were cast in Kowloon East. It's a constituency of four seats, which meant the quota was 59,061 votes. The top candidate on any list that got that many votes automatically won a seat. If the party was to hit the quota twice by winning 118,122 votes, the second candidate on the list would also automatically take a seat.

If the ticket still had votes after that, it would then compete for an additional seat against other tickets that drew fewer than 59,061 votes. Those with the highest number of votes - their remainder vote - would take the seats.

If the government's proposal was now in place and an incumbent lawmaker from Kowloon East resigned or died, League of Social Democrats chairman Andrew To Kwan-hang, who got 28,690 votes in 2008, would fill the vacancy.

What if that next-ranking candidate had died, or didn't wish to serve? Under the government proposal, the candidate with the second-largest number of remainder votes would fill the vacancy. Under this hypothesis, if To turned down the chance to serve, the seat would go to the Democratic Party's Wu Chi-wai, who won 16,363 votes in 2008.

If a second vacancy then arose in Kowloon East, the district might be in trouble. None of the candidates on any of the six tickets that contested the constituency in 2008 would have any 'remainder votes' to fill the vacancy. That's because in 2008 not a single list in Kowloon East met the quota of 59,061 votes. The four winning candidates were those at the top of their respective lists that were allocated seats under the largest-remainder formula.

A spokesman for the Constitutional and Mainland Affairs Bureau said: 'In the case of the Kowloon East constituency, using the result of the general election in 2008, the two candidates who could succeed a potential vacancy would be Andrew To and Wu Chi-wai. We expect that such succession arrangement in practice would be adequate to deal with vacancies which may arise in future.'

The spokesman did not respond to the scenario of a second legislator resigning or dying in office after Wu had filled a vacancy midterm.

Ma, the Chinese University professor, said such a 'ridiculous scenario' was possible under the government proposal. He sees other flaws, too.

'The government's argument that once a serving legislator resigns, his votes should go with him as he has already 'used' the quota of the votes to take up his seat is totally wrong,' Ma said. 'Under the proportional representation system, voters cast their votes for parties or a list of candidates, rather than for individual candidates. The government's argument appears to assume the votes for a lawmaker who resigns midterm would disappear after his departure. That kind of logic is ridiculous.'

The proposal appears to put Hong Kong out on its own internationally.

According to a study by the International Institute for Democracy and Electoral Assistance, if a seat becomes vacant between elections in European countries such as France, Austria, Germany, Denmark and the Netherlands, which also have party-list proportional-representation systems, the vacancy is filled by the next candidate on the list of the former representative's party.

In Sweden, Ireland and Belgium, those vacancies are filled by substitutes named on the relevant lists.

In a paper submitted to Legco's panel on constitutional affairs, the Constitutional and Mainland Affairs Bureau admitted that in countries where the proportional representation system was practised, it was common to fill the vacancy with the first candidate not elected on the party list of the representative whose death, resignation or incapacitation led to the vacancy.

In an attempt to justify its proposal, the bureau could cite only the example of the replacement mechanism adopted in the Tasmanian House of Assembly.

There, members are elected by proportional representation under a single transferable vote system. (The single transferable vote is designed to provide proportional representation in multicandidate elections. The system initially allocates an individual's vote to their most preferred candidate. Votes left over once that candidate has been elected, or votes which are unused, are transferred to other candidates, or eliminated, according to the voter's stated preferences.)

Any vacancies are filled by examining the ballots cast for the member whose death, resignation or incapacitation triggers the vacancy to determine which other candidate those who voted for that person favoured most.

Ma noted that the electoral system in Tasmania is different from the system in Hong Kong. 'Voters in Tasmania choose individual candidates, rather than a party list,' he said.

In defence of its proposal, the Constitutional and Mainland Affairs Bureau said electors in Hong Kong cast their votes on the basis of the lists headed by candidates who were well known.

'Hence, the number of votes obtained by a list of candidates to a significant extent hinges on the presence of individual well-known candidates,' the bureau said. 'Thus, once a candidate has resigned, it is reasonable to assume that in the absence of that candidate, his list may not receive the same level of support. 'Once an incumbent Legco member resigns, his votes should go with him as he has already used the quota of the votes to take up his seat.'

Horacio Boneo, who has served as a consultant on elections for the United Nations and the International Foundation for Electoral Systems since 2000, said the Hong Kong government, while taking an unusual stance, had a valid argument that the number of votes obtained by a list of candidates was directly related to the presence of individuals of renown.

Wong Kwok-kin, a lawmaker from the Federation of Trade Unions who was returned in Kowloon East in 2008, said the government proposal would unfairly undermine the representation of parties if lawmakers die or become too ill to serve.

'If I fail to discharge my duty because of serious illness, it would make more sense to allow the candidate who ranked the second on our list in the 2008 election to fill the vacant seat,' Wong said. 'Otherwise, our federation would lose representation in Kowloon East.'

Wong believes Hong Kong should follow European countries with proportional representation systems and fill a vacancy with the next candidate on the list of the former representative's party. But he said the federation supports the government proposal and he would comply with its stance when the proposal is put to a vote in the legislature.

The proposal would take effect next year and apply to geographical constituencies and five new seats in the district councils functional constituency that will be filled by citywide election.

Ma's colleague at Chinese University, political scientist Ivan Choy Chi-keung, faults the government proposal for failing to ensure a party maintain its representation if their representative dies in office.

'The introduction of proportional representation in Western countries was intended to facilitate the development of parties, but what we are doing in Hong Kong is to discourage or even undermine their development,' he said.

3

The number of by-elections held for Legco seats since 1997

- December 2000 (one seat)

- December 2007 (one)

- May 2010 (five)