I have on a number of occasions described this exercise as the most challenging task of my public service. To me, it is not just my duty but a mission to mark a historic milestone in Hong Kong's constitutional development.

Over the past 20 months, I have taken part in 124 consultation sessions and forums and about 20 district visits to inform the public of our proposals. I have met the media on around 100 occasions to answer questions. And I have had numerous meetings with legislators, professional bodies and academics.

The path for the democratic development of Hong Kong since the return to the motherland has been full of twists and turns. We have had some successes and some failures.

For 20 months, the Task Force on Constitutional Development, which I head, has regularly explained that the constitutional development of Hong Kong must be based on the Basic Law and relevant interpretation and decisions of the National People's Congress Standing Committee. Any deviation from this clear-cut constitutional basis is just like building a castle in the sky. It has no solid foundation, and it cannot fly.

Despite our concerted and sincere efforts, some pan-democratic legislators and political groups still refuse to accept the constitutional basis of our proposals. This is worrying.

Sometimes, government officials and legislators disagree on policies or issues. Yet, we invariably want the best for Hong Kong people. In the back of my mind, always, is the firmly held belief that public policies must serve the long-term interests and well-being of the community at large.

I believe that the government's proposal serves the long-term interests of both the country and the Hong Kong special administrative region.

We have devised a proposal that is open, fair and competitive. It responds to the strong aspiration for universal suffrage and strikes a balance among diverse views. The proposal helps us reach the goal of selecting the chief executive by universal suffrage in a way that best meets Hong Kong's unique and actual situation.

The proposal includes three liberal and democratic features.

First, it has a lower nomination threshold to encourage competition. Each person seeking nomination would need no fewer than 120 but no more than 240 recommendations from the nominating committee. This system allows at least five and at most 10 places for those seeking nomination. It not only provides the committee with more choices but also makes the nominating procedure more competitive.

Second, nominating committee members may vote for as many chief executive hopefuls as they deem worthy - at least two, but up to 10. This will make the process more competitive.

Third, the ballot will be kept secret to ensure free choice. Since nominating committee members will not have to disclose their choice, they can vote for their preferred candidates according to their free will and with no pressure.

This universal suffrage proposal is constitutionally and legally in order, fair and reasonable. Compared to the current method of selecting the chief executive by a 1,200-member Election Committee, the government's proposal is undoubtedly a big step forward for Hong Kong.

To justify their decision to veto the proposal, pan-democratic legislators have often claimed that, once passed, the electoral method would be in place forever and that there would be no room for further improvement.

Let me, once again, state the facts of the matter. Article 7 of Annex I to the Basic Law and the interpretation by the NPC Standing Committee in 2004 have clearly established the legal basis and procedures to initiate further amendments to the selection method. So, the selection method is not cast in stone.

Another frequently used justification for a veto is that the Hong Kong government has failed to fully convey the views and aspirations of the public (in particular those of the pan-democratic legislators) to the central authorities, and therefore we should restart the entire process.

The reports submitted by the chief executive and the task force to the NPC Standing Committee in July 2014 reflected truthfully the views received during the consultation.

In addition, before the Standing Committee's August 31 decision, the Hong Kong government arranged four meetings last year between all Legco members and the central government officials responsible for Hong Kong's constitutional development. Clearly, legislators had the opportunity to express their views directly to these officials.

In the Legco chamber, the pan-democratic legislators sit opposite government officials. But it does not follow that we always take an opposite stance. On social issues relating to people's livelihood, we often manage to find common ground after heated discussions.

For constitutional development, our views on the actual method to select the chief executive by universal suffrage may differ, but we are all working for the democratic development of Hong Kong. I hope we can set aside our differences and strive to achieve a goal shared by all.

We must seize this opportunity to secure endorsement of the reform proposal. We have a real chance, a historic opportunity, to realise our dream of selecting the chief executive by "one person, one vote" in 2017. We must not let it slip away.

I sincerely urge pan-democratic legislators to think twice about their vow to vote down any proposal based on the August 31 framework. Many public opinion surveys have found more supporters than opponents of Legco passing the government's proposal. I hope the pan-democrat legislators can respect the wishes of the majority of Hong Kong people.

Hong Kong's democratic development is at a critical juncture. I am worried that violent protests will again be staged when we put the proposal to a vote. In this regard, I urge all protesters to express their views calmly and peacefully.

I am, of course, also worried about what might follow if the proposal is vetoed. For a start, our democratic development would come to a standstill. The community and legislature would remain divided. In the end, all Hong Kong people would suffer.

As a Hongkonger, how can I possibly be indifferent to such a scenario?

I hope that our pan-democratic legislators will carefully weigh the consequences and vote to support the proposal. I do believe Hong Kong's 5 million eligible voters want the chance to elect their chief executive. For Hong Kong to take this historic step, I appeal to all the pan-democrats to show your political courage and make the right choice.

Hong Kong needs your vote for the proposal to implement universal suffrage for the chief executive election.