John Key has revealed that a new bottom-line will apply to his Government this winter: one of the 34 new BMW limousines being bought for Cabinet ministers will come with the optional extra of heated seating.

The Internal Affairs Department, which purchased the vehicles, has consistently refused to divulge details of their cost on the grounds it is commercially sensitive.

However, BMW's New Zealand website lists installation of rear heated seating as adding close to $1000 to a vehicle's price.

The car, which will be based in Dunedin, is one of three in the package being designated for "long-distance and long-duration movements".

The Prime Minister - who is also the Minister responsible for Ministerial Services - revealed that the Government had taken up the optional extra in an answer to a written parliamentary question from Labour MP Chris Hipkins.

Mr Hipkins yesterday said that if the Government was serious about cutting wasteful spending, it should cancel the purchase of the new BMWs or at least say no thanks to the heated seats and other "nice to have" trimmings.

"We've got hundreds of families in Christchurch who will have to go through the winter in cabins and campervans. A heated seat or two there wouldn't go amiss."

The three long-distance cars will also be fitted with mobile office facilities, including monitors, internet access and back-seat lighting. The vehicle destined for Dunedin will service the South Island, while the other two will be based at Palmerston North and Hamilton and service the North Island.

Replying to a question in February from the Greens' Sue Kedgley, Mr Key said the cars would not have optional extras such as "massage chairs to relax the occupants' shoulders and lumbar spine", separate air-conditioning units, high-performance audio speakers and automatic closing doors.

However, Mr Hipkinshad asked if all of the 34 new BMWs ordered had the same features and options.

He said the Government's hypocrisy was staggering. "This is a Government which is preparing a harsh Budget that will strip funding from much-needed public services and they keep telling everyone else to tighten our belts. But they've still found the money to buy themselves 34 new BMWs with all the trimmings."