Prime Minister John Key and his ministers have developed a taste for air force travel, with their use of RNZAF aircraft more than doubling in a year, according to Defence Force documents.

Evidence of the Department of the Prime Minister and Cabinet's increasing use of air force aircraft came as Mr Key copped flak yesterday over his use of an Iroquois helicopter to get from Auckland to the V8 Supercar races in Hamilton and back in time for a golf club dinner.

Budget documents show the RNZAF allows 70 flying hours in its Boeing 757 aircraft for the use of the department each year, 25 hours of Iroquois flying time, and 100 hours for the 11-seat King Air aeroplanes.

The Defence Force's 2010 report shows the department used 82 flying hours across all three aircraft types. Just 32.2 hours were used in 2009.

Labour leader Phil Goff and Greens co-leader Metiria Turei said yesterday that the Prime Minister's round trip on Saturday was an unnecessary extravagance at a time when many New Zealanders were feeling the pinch from the Government's policies.

A spokesman for Mr Key said the decision by his staff to use the helicopter was made because of concerns heavy traffic at the car races could delay the PM getting to a black-tie dinner at the Royal Auckland Golf Club.

Mr Goff said that at a time Mr Key's Government was cutting back Defence Force spending, "having the force spend unnecessarily high amounts of money on VIP transport would not be my priority for expenditure".

Speaking from his car as his wife drove him back to Auckland from an event at Karapiro, Mr Goff said although he was entitled to VIP travel, his trip would cost the taxpayer no more than the price of the petrol.

"If it's good enough for me as Leader of the Opposition to say when times are hard we've got to watch what we're spending, then it's good enough for the Prime Minister to do the same.

"The Prime Minister's got to examine his conscience as to why he's cutting back on things like home care for the elderly but somehow it's okay for him to go to a photo opportunity in a helicopter."

Labour deputy leader Annette King said flying an Iroquois cost about $900 an hour. The Defence Force was unable yesterday to say how much Mr Key's trip would have cost.

Ms Turei said the cost could not be justified by Mr Key, "at a time when he's telling New Zealanders they have to tighten their belts and he's cutting funding to critical social services and cutting public service jobs".

Mr Key's office said it would have been unacceptable for him to be late for the golf club dinner as the Governor-General was also attending and protocol required that a PM could not arrive later than the Queen's representative.

"When we use the air force, more often than not it is because that's the best logistical option we have that fits with the timing requirement of the Prime Minister's schedule."

Mr Key's office said the 113km flight took about 45 minutes each way. By car the journey is 130km and - traffic allowing - takes about 1 and a half hours. Racegoers who returned to Auckland after the last race finished at 4.30pm reported traffic was relatively light.

In 2009, Mr Key was criticised for using two Iroquois to fly from Blenheim to Kaikoura so he could launch a Whale Watch boat.

However, the use of RNZAF aircraft by him and his ministers has fallen well within the air force's budget in the past two years.

Use of RNZAF aircraft was higher when Helen Clark was Prime Minister. She was criticised for using a King Air plane to get to a Grey Power meeting in Southland in 2008 when commercial air traffic was disrupted.

Use of air force aircraft hit 326.2 flying hours in 2003 when ministers and VIPs were flown to war commemorations in Korea and Italy, on an official visit to the Solomon Islands, visits to Defence Force personnel in the Middle East and to the Commonwealth Heads of Government Meeting in Nigeria, among other trips.

Additional reporting: NZPA, Newstalk ZB