Prime Minister Stephen Harper has been flying in military jets to Conservative events and even a hockey game — despite having once railed against their use by the previous Liberal government.

Invoices obtained by the Canadian Press show Harper flew Challenger executive jets three times in 2006 — and the Conservatives only fully reimbursed the military for one of the flights, which are estimated to cost more than $2,000 per hour.

Other prime ministers — like Conservative Brian Mulroney and Liberals Jean Chrétien and Paul Martin — took Challenger jets to government events and to events on behalf of their respective political parties.

However, opposition politicians were quick to accuse Harper of being a hypocrite on Wednesday, recalling his past comments such as a 2005 jab at Martin and his Liberal government.

"As they pad their expense account and look out the windows of their $11,000 per hour Challenger jet flights to B.C., they think that everything is going pretty well," Harper then said. "They just don't get what real life is like for ordinary Canadians."

According to invoices obtained through the Access to Information Act, Harper and six staff members used a military jet to fly from Ottawa to Moncton, N.B., for a Conservative event on July 26.

The Conservative party paid the Defence Department $3,144.18 for the trip — half of what the flight was estimated to cost.

The Prime Minister's Office, in an e-mail to the Defence Department, explained that it settled on the $3,144.18 price tag after consulting with a travel agent and determining how much it would have cost the group to fly on a regular commercial airline.

Another invoice says that on Oct. 4, Harper, his son and five staff members flew to Toronto to watch a Maple Leafs hockey game and paid the commercial rate once again.

Only on a Feb. 10 flight from Ottawa to Halifax, for a retirement party after John Hamm stepped down as Nova Scotia premier, did the Conservative party pay for the full cost of the jet, an invoice shows. On that invoice, the military outlined the cost, stating the flight cost $2,139 per hour.

PM must take jet for security reasons: spokeswoman

A spokeswoman for Harper said the prime minister must, for security reasons, take the jet. She said the decision to pay commercial rates was made after discussions with various government departments and the private sector.

"There was no previous protocol, as the former Liberal government never reimbursed Canadian taxpayers when they used the Challenger for non-government business," Sandra Buckler alleged in an e-mail to the Canadian Press on Wednesday.

People on Martin's staff denied the charge Wednesday night, telling CBC News they have documents to prove they reimbursed the military for the use of the Challengers.

Harper's staff told CBC News that the Liberals took the jet far more often than the Conservatives.

"Aside from the [Feb. 10] instance, Canada's new government has been consistent in its protocol for reimbursing the cost of an economy return trip ticket," Buckler told the Canadian Press. "We believe this is a fair balance, given the fact that the prime minister, for security purposes, must travel privately."

Liberals miffed by $11,000 price tag

The $11,000 price Harper quoted in the 2005 speech is five times higher than what the military billed Harper in 2006.

Harper's staff told CBC News that they were just estimating the $11,000 cost in 2005.

The Liberals were especially miffed by the $11,000 estimate. "They're trying to say they're whiter than white," Liberal MP Denis Coderre told the Canadian Press. "But it's worse because they're playing with the numbers."

The Canadian Press noted that it is difficult to calculate the actual cost of a flight on the jet. Military documents, obtained through Access to Information, suggest the cost of operating the jets range from $9,124 to $11,541 per hour.

However, most of the money is a fixed cost that accrues whether the jet is flying or not, making it hard to nail down a billable hourly rate.