SINGAPORE - Businessman Ho Kwon Ping has called for limits to Singapore's Internal Security Act (ISA), under which people can be detained without trial if they are deemed to pose a threat to national security.

The one-time political detainee also called for the phasing out of caning and capital punishment, and the introduction of National Service for new male citizens and Singaporean women.

In a lecture on security and sustainability on Thursday, he said Singapore must evolve to keep up with changing social values.

"A willingness to change with the times... can prevent the intellectual rigidity which weakens the sustainability of our society as a dynamic and evolving culture," he said in the third of five Institute of Policy Studies-Nathan lectures.

Mr Ho, the first S R Nathan Fellow, suggested gradually liberalising old policies.

A former journalist, he was himself detained under the ISA in 1977 for writing articles with a pro-Communist slant. But on Thursday, he held back from calling for the Act's abolishment.

Instead, he suggested reducing the initial detention period to one year - down from the current two - and putting in more rigorous checks and balances for the subsequent detention periods.

As security threats evolve, with Islamic radicalism casting a shadow over the world today, Singapore needs to find a balance between the Government's power to clamp down on such threats and the space that civil society needs to express its views without the fear of detention, he said.

In fact, preventive detention - once heavily criticised - has become "grudgingly accepted" by Western governments as they face up to the looming threat of terrorism, he said.

And calls to abolish it have been watered down to calls to ensure unconstrained power is not abused.

"What must not change is the constant awareness that any people who surrender too much extra-ordinary powers to any Government, does so at its own peril," said Mr Ho.