Has the London Murder rate fallen by a quarter under Boris?

"Murders [in London] have fallen by an average of 25 per cent."
Boris Johnson, press release, 14 January 2011.

The nebulous battle for the London Mayorality returned to familiar territory last week as the incumbent Mayor Boris Johnson claimed that the latest Metropolitan Police crime statistics vindicated his record on violent crime.

Commenting on the London Evening Standard's reporting of the story, Mr Johnson argued that the number of murders committed in the capital — the lowest since 1978 — represented an 'average' fall of a quarter.

This is an odd claim for a number of reasons, the most striking of which is that the Mayor doesn't qualify what he means by 'average: is it an average fall of 25 per cent per week? Month? Year? Or perhaps an average fall per borough?

Having used his Telegraph column yesterday to call for the blogosphere to hold politicians to account, Full Fact took Boris at his word and probed his claim further.

It must be said that the London Mayor has some previous when it comes to crime statistics. We looked at a raft of crime claims made by Mr Johnson when he announced his intention to stand for re-election last year, and found that his figures did not match the official ones.

Looking at the Metropolitan Police crime tables — the source of the Standard story on which the Mayor was commenting — reveals that in the 2009/10 financial year there were 113 murders in the 32 London Boroughs, compared to 146 in 2008/09 and 156 in 2007/08, the last year of the previous administration.

There was therefore a 6.4 per cent fall in the number of killings in Mr Johnson's first year in office, and a 22.6 per cent fall in his second. On these terms, an average fall in the number of murders for the first half of the Mayor's inaugural term would be 14.5 per cent.

However the total reduction in the annual number of murders that has occurred since the 2008 election (43) does represent a 27 per cent improvement on the situation Mr Johnson inherited.

The Met themselves collate the most recent sets of crime statistics on a monthly basis, so there remains a question over whether the Mayor's figures represent the fullest portrayal of the 'average' decline in killings. The average monthly fall over the last 24 months was 11.8 per cent, with an average fall of 16.6 per cent in the 2009/10 period and a 4.96 per cent fall in the 2010 calendar year.

So whilst Mr Johnson's use of the word 'average' remains a curious one, it does appear that there is at least one reading of the statistics that backs the Mayor up.