DRIVER'S SEAT: An air force Iroquois helicopter flew John Key from Mechanics Bay, Auckland, to Waikato Stadium for the V8 races, and then back again.

Prime Minister John Key's office is blaming heavy traffic for booking an air force helicopter to ferry him to and from the V8 races so he could make it home in time to change for a black tie dinner.

But Labour MP Trevor Mallard said yesterday the trip was extravagant and insensitive, given the Government's drive for belt tightening across the state sector, including the armed forces.

A spokesman for Key confirmed yesterday an air force Iroquois helicopter flew the prime minister from Mechanics Bay in Auckland to Waikato Stadium for the V8 races in Hamilton, then back to Mechanics Bay at 4.45pm.

Key had to go home to change for a black tie dinner, with his pick-up scheduled for 6.30pm. The dinner was to celebrate the Royal Auckland Golf Club getting Royal status and Key attended with the Governor-General.

''The decision was made to use the helicopter because of concerns about traffic issues at major events...it was believed that transport issues would have meant he could have been late for the next event, which (would be) unacceptable because the protocol is that he cannot arrive later than the Governor General.''

But Mallard said the trip between Auckland and Hamilton was not a long one and there was no sense of emergency.

''We've known now for at least a year ... the dates of the V8s and if he had a half competent organisation he would have allowed proper travel time between his appointments.''

He did not accept the prime minister's response ''which sounds like rationalisation for a very expensive and insensitive use of taxpayer funds."

In 2008, former prime minister Helen Clark came under fire from ACT for using an air force flight on the campaign trail after commercial flights to Southland were cancelled.

National declined to criticise Clark at the time.