Leung Chun-ying faces an uphill battle trying to roll out his free education plan before his term ends in 2017 because of the complexity of subsidising kindergartens, educators say.

The chief executive pledged in his election platform to offer 15 years' free education to every child. Leung is expected to announce in today's policy speech a committee to study extending school subsidies to pre-primary levels and boosting the existing kindergarten voucher scheme.

Under the scheme, launched in 2007, parents of children aged three to six can apply for a voucher worth HK$16,000 a year to put them through any of 750 participating kindergartens.

At meetings held in December between educators and officials it was revealed the committee, to be set up in summer, will tackle the tricky task of how to channel subsidies equitably to preschools, many of which operate from private premises such as shopping malls.

"There are issues that require thorough analysis. Implementing a policy like this can easily take three years," said Lam Chui-ling, head of a kindergarten in Kwai Chung. "The government is dedicated to doing it, but it may not be able to implement it in this term," said Lam, who attended one of the meetings last month. When asked for details of the free education plan, Secretary for Education Eddie Ng Hak-kim said yesterday he had been meeting with various stakeholders since July but the policy was too complex to rush. "We understand the expectations. And we hope that within the [next] five years, as the chief executive pointed out during the election, we can meet such expectations [for free education]," he said.

But the Federation of Education Workers, a pro-government teachers union, said there was no time to lose. "It will be too late to do it only when Leung's term nears an end," vice-chairman Wong Wai-shing said.

But rent subsidies for kindergartens would prove a difficult area, Wong said. "Rents in shopping malls can go up indefinitely and rents are related to overall costs and school fees," he said.

Wong said the government should first extend the kindergarten subsidy scheme and boost teachers' pay to retain talent.

Meanwhile, a government source said Leung would not announce an increase in the number of undergraduate places in his policy address - despite repeated calls from educators.

And Leung's popularity continues to fall. It is down 0.2 points to 48.9, with a net approval rating of minus 20 percentage points, the latest University of Hong Kong opinion poll shows.