OTTAWA - Drivers hired to shuttle federal cabinet ministers around Ottawa charged taxpayers more than $600,000 in overtime above their annual salaries last year, a CTV News investigation has found.

An analysis of timesheets for each minister's driver -- from April 1, 2010 to March 31, 2011 -- reveals that almost every chauffeur racked up hundreds of overtime hours, with payouts averaging more than $20,000.

Each of Prime Minister Stephen Harper's 26 ministers and 11 junior ministers that year -- a total of 37 -- were entitled to a car and driver, who were paid between $46,883 and $50,755.

The chauffeur for one minister rang up a tab of more than $40,000 above his annual salary.

Sedans and SUVs, often black with tinted windows, can be seen all over the capital. Drivers sit around waiting for their bosses to come back from a meeting or lunch, ready to ferry them in the back of a taxpayer-supplied set of wheels.

But this perk comes with a hefty price tag.

The drivers' paperwork, obtained by CTV News under the Access to Information laws, shows that it wasn't uncommon for them to put in at least 20 hours a week in overtime waiting for their bosses.

The analysis reveals that the drivers who serve the Public Works and Government Services Minister Rona Ambrose accumulated the most overtime: more than 1,000 hours costing taxpayers $40,074.

Driver on standby for Clement

Records show that Tony Clement, then Industry Minister, had a driver on standby for more than 360 days that year.

The driver charged taxpayers to be on "standby" for Clement virtually every hour outside of his regular shift -- 16 hours every weekday and 24 hours on weekends to a total of 6,548 hours in 2010/11. (Standby hours are paid out at 0.5 hours for every four hours on standby).

Clement, who is now the Treasury Board President and in charge of the public purse, defended his use of the vehicle.

"Ministers work long hours," he said. "Frequently drivers have to work the hours that a minister is working because they have to be on standby."

He adds he is "always looking for ways to deliver better services for less" to Canadians.

"Is there a better way to deal with these employees and to deal with the requirements of ministers who work long hours?" he asked. "That is a very good question, so we certainly would take that under advisement."

Meanwhile, the documents show Human Resources Minister Diane Finley's driver had 951 hours in overtime.

Finance Minister Jim Flaherty's driver received a payout of $34,941.14 that year.

The driver for Agriculture Minister Gerry Ritz racked up more than 700 hours in overtime, valued at almost $29,000. The driver for embattled International Co-operation Minister Bev Oda received nearly $23,000 for 600 hours in OT.

Drivers' overtime is paid at 1.5-times or double the hourly rate. Most drivers elect to receive a cash payment for putting in that extra duty, but they do have the option to take it as time off. Drivers also receive a "meal reimbursement" of $10 to $20 each time they work more than three hours of overtime.

'Mr. Clement needs to explain'

Opposition critics decry the spending as a waste of public money, especially while the federal government begins to eliminate 19,000 public service jobs.

"We're having front line workers laid off because Mr. Clement feels they are unnecessary," said NDP ethics critic Charlie Angus. "I think Mr. Clement needs to explain to taxpayers, once again, why he should be trusted with ensuring belt tightening."

Liberal MP Mark Eyking says the expense shows the government "is on a bit of an ego trip."

"They like to have the cars running to make them look like big shots but the taxpayers are paying for it."

But Ministers have the option of classifying their drivers as ministerial support staff and don't get paid overtime.

The paperwork shows that only three ministers listed their chauffeurs as exempt: Defence Minister Peter MacKay; former Veterans Affairs Minister Jean-Pierre Blackburn; and Julian Fantino, who was the minister of state for seniors in 2011.

And one minister -- Gary Lunn, who was the former minister of state for sport -- opted not to hire a driver at all, even though he was entitled to one. Lunn told CTV's Ottawa Bureau Chief Robert Fife that he "preferred to walk" instead of using the government vehicle.

Three departments refused to provide details on drivers' overtime citing privacy reasons: Environment Canada, Public Safety Canada and the Privy Council Office.

The CTV analysis didn't take into account the fleet of vehicles for the prime minister. Unlike members of his cabinet, for security reasons, Harper must travel in government vehicles.

CTV used the lowest figure in the drivers' salary range in calculating the dollar value of the overtime.