How many statistical misdemeanours does the new Government have to commit before it is shown the red card?

This week the Prime Minister was reproved in a letter from the head of the UK Statistics Authority for repeating Conservative claims about increases in violent crime.

In the Commons on 7 July, David Cameron said gun crime and violent crime "went through the roof" under the last government. They had almost doubled, he said.

It is the same charge made by Chris Grayling MP before the election but it rests on a shaky reading of the statistics. Sir Michael Scholar, chairman of the Statistics Authority, said in a letter to Alan Johnson MP, who had complained to him about the Prime Minister's remarks, that changes made to the way police recorded violent crime in 2002-03 made it "not possible, without qualification" to compare police-recorded statistics from the late 1990s and now.

A better source of data is the British Crime Survey. The latest figures, released this week, show a 42 per cent drop in violent crime since 1997, and a 51 per cent drop in violence with injury. Police-recorded violence, after the hiccup caused by the change in recording, shows a similar trend in the past four years. Of course, people don't believe these figures. Two thirds believe crime is rising. Perhaps they've been listening to Mr Grayling and Mr Cameron.

The crime claims come on top of a peculiar exercise by the Cabinet Office, which decided to count the number of civil servants employed by government departments – via a haphazard ring-round, by the look of it – when a perfectly good count by the Office for National Statistics already exists.

But the worst example of all was Sir Alan Budd's intervention on the loss of jobs likely to be caused by public sector cuts. Sir Alan runs the Office of Budget Responsibility, supposedly an independent agency. Not only were his figures misrepresented by the Prime Minister in the Commons but their publication was advanced by a day so that Mr Cameron could flummox the Opposition. This strikes me as a flagrant breach of the Code of Conduct on official statistics, although Sir Michael has yet to pronounce on it.

But isn't this what politicians always do? In the past, yes. But in the latter years of New Labour, even those sultans of spin felt embarrassed enough to lay down some rules and establish the Statistics Authority to police them.

Statistics are not the property of the government of the day: we pay for them to be collected and we're entitled to see them used honestly and fairly. The new Government needs to learn this fast if it is not to shred its own credibility.

Nigel Hawkes is director of Straight Statistics (www.straightstatistics.org)