The timing of the purchase of 34 new BMWS to replace the three-year-old Beemers in the Government's fleet is embarrassing for the Prime Minister, particularly because he appears to have known nothing about the impending purchase or the details of the contract. This despite the fact that members of his own team sit on a committee that was informed that the cars would be replaced.

If it's any consolation to the public, the cars the New Zealand ministers and their guests will be riding round in come without the sunroofs, fridges, liquor cabinets or televisions that are optional features of the 7 series. And when the first fleet arrived in 2008, they were believed to have cost around $90,000 each - far from the figure of $200,000 that has been bandied about.

It makes a certain economic sense to trade in a car once it's out of its warranty - if you can afford to. Cars start costing money the minute they leave the showroom floor and I would hate to think of the expense of running repairs for 34 top-of-the-line BMWs.

However if, as BMW says, one of the reasons Internal Affairs awarded the contract to them was because of the cars' "extremely low whole-of-life costs" then you'd think they'd have planned to hang on to them for slightly longer than three years.

Ministerial cars keep their value though: look at the 1985 Ford LTD that David Lange used to drive around in. It's on Trade Me for 12 grand; another from the same year that never made it as a Crown car is going for only half that.

The replacement of the cars also partially explains why long-serving MPs start developing a sense of entitlement. If they are given reasons and justifications as to why they must have top-of-the-line, brand-new vehicles, eventually they'll come to think they deserve them and that they'll break out in hives if they park their bums on the seats of anything less than a gleaming showroom-condition vehicle.

They'll conveniently forget just who's picking up the bill.