OTTAWA - The mandatory, long-form census fills a vital need that outweighs concerns about intrusiveness, a former senior public servant said Friday.

Mel Cappe, once the country's top civil servant as clerk of the Privy Council who later served as high commissioner to Britain, urged MPs on a Commons committee to find a way to save the long census.

"The long-form census is a public good," said Cappe, who now is president of the Institute for Research on Public Policy.

He said the threat of jail for failing to fill out the long form should be removed and the questions should be tweaked to minimize the intrusiveness, but the long-form should be kept.

The data collected in the long form is vital to governments, community groups and businesses and is most effectively collected by the state, he said.

Among other things, the information allows governments to help particular social groups and build infrastructure where it's most needed.

"We need a data base that we can trust."

Cappe was one of a parade of witnesses who urged MPs on the committee to save the mandatory long census form.

The day-long Commons committee heard from think tanks, native groups, community groups and individuals. Most of the organizations solidly supported retention of the long form, although a number of individuals backed the idea of scrapping the form.

The Harper government has scrapped the mandatory long questionnaire as too coercive and intrusive. They want to make the long form voluntary, but distribute it to more households. The government also wants to add some questions to the still-mandatory short census form.

No good, witnesses said. They said the voluntary nature will bias the data.

"We believe the announced changes would harm the integrity and quality of the Canadian statistical system," said Ian McKinnon of the National Statistics Council.

He said the long form provides a vital benchmark that is used as a basis for other data collection systems, including the labour force survey which looks at unemployment. Without that benchmark, the validity of the jobless data is questionable.

He agreed with Cappe that Statistics Canada should weigh the value of each question against people's expectations of privacy.

James Turk of the Canadian Association of University Teachers said the census is a collective responsibility.

"It's essential for the federal government, provincial governments, municipal governments, businesses to have reliable and valid information," he said.

"Eliminating the long-form census is a disservice to every single Canadian."

James Henderson, a farmer appearing as an individual, said he found the long form "burdensome," but he was almost alone in his support of the government's decision.

The Liberals have promised that when the Commons returns next month they will introduce a private member's bill to restore the long form and forbid governments from interfering with the census without the consent of Parliament.