The government faces several hurdles as it plans for the 2017 chief executive election. The Legislative Council must vote by a two-thirds majority for the electoral reforms to be approved, so it must win the support of at least some pan-democrats. Beijing must approve the final proposal.

"With concerted efforts by all of us, differences can be narrowed step by step and consensus forged bit by bit," Lam told lawmakers. Neither Lam nor the 57-page consultation document made any direct reference to the idea of public nomination.

But in response to a question by Beijing-loyalist Tam Yiu-chung, Lam said proposals falling outside the Basic Law would "divert from the focus of the consultation and be a waste of time". Article 45 of the Basic Law puts the power to nominate candidates in the hands of a "broadly representative" nominating committee, acting "in accordance with democratic procedures".

The consultation document, which also covers the 2016 Legco election, says any proposal that "bypasses the nomination procedures of the nominating committee" or undermines its power to nominate candidates might not conform to the Basic Law.

An administration source said the government was willing to listen to all ideas, including public nomination. "But the public have to justify how those proposals can comply with the Basic Law," the source said.

A poll released last night showed that 66 per cent of respondents favoured "public nomination" when asked late last month, up from 62 per cent a month earlier. The University of Hong Kong poll of about 1,000 people was conducted for the Alliance for True Democracy.

Lam said the requirement that the leader "love the country and love Hong Kong" was not covered by the consultation because it was self-evident that the chief executive would meet this requirement.

Pan-democrats fear it will be used to justify keeping critics of Beijing out of the race.