A further analysis of recently released GPS data from the Government's fleet of ministerial limousines is giving fresh evidence as to why, perhaps, officials really didn't want their details exposed to public view. For not only does the data expose a pattern of repeated speeding infringements by the cars, it also gives some valuable insights into how they are used.

In this case the period to which the GPS data applies covers the time around last year's Northland by-election campaign. A time during which the Government's opponents accused Ministers of a making liberal use of the taxpayer funded Crown cars on the election campaign. A close look at the data, albeit that it only covers times when the cars broke speed limits in the electorate, does seem to suggest those criticisms had some foundation.

The data shows that the Crown cars were used on at least 25 occasions covering 18 days in the eight weeks preceding the March the 28th polling day. When you compare that to the four months that followed, when there are only records of the cars being in the electorate 10 times, it does strongly imply the Government upped the ante in terms of their use.

The disclosure is one that's raised the ire of the man who won the Northland by-election, New Zealand First Leader Winston Peters. After having to use party funds to pay for a campaign bus during the election, he's singularly unimpressed that his opponents managed to travel around the electorate during the campaign with taxpayers picking up their tab.

Why is this an issue? Well ministerial cars and ministerial funding are supposed to be used for ministerial purposes only. Election campaigns don't come within cooee of that definition.

However our politicians, both of this Government and those previous, evade this by timing ministerial announcements to coincide with election events. That way they can claim, and in this instance Cabinet Minister Steven Joyce certainly has, that the cars are being used for ministerial purposes. It's cute, and highly convenient, way of allowing the Government of the day a head start when it comes to campaigning.

Is it legal? Technically it probably is. Is it ethical? Probably not. Particularly if your party has previously taken a stand against taxpayer funded election campaigns.

Something the National Party has done.

Felix Marwick is Newstalk ZB's Chief Political Reporter