Gordon Brown has been accused of deliberately misleading the public by claiming that not retaining genetic profiles of innocent people on the National DNA Database (NDNAD) would have led to 114 murderers getting away.

The charge was made on Friday by the genetics lobby group GeneWatch UK. It analysed a speech the Prime Minister made on June 17 where he argued for the retention of DNA profiles from thousands of charged suspects, including children, in criminal cases that were later found not guilty or never made it to trial.

A Downing Street spokeswoman said: "I think in this case we'll have to let the Prime Minister's words speak for themselves. The figures he quoted were publicly available from 2006." The Home Office had referred The Register's questions about the speech to Number 10.

The massive expansion of the NDNAD was mandated by the Criminal Justice and Police Act 2001. GeneWatch's Dr Helen Wallace accused Brown of knowingly manipulating statistical estimates to spin them as facts in support of storing innocent people's genetic information. In a statement she said: "Gordon Brown has stooped to a new low."

Match making up

In his speech on "Liberty and Security" at the Institute for Public Policy Research, Brown said: "If we had not made this change [retaining innocents' DNA profiles], 8,000 suspects who have been matched with crime scenes since 2001 would in all probability have got away, their DNA having been deleted from the database.

"This includes 114 murders, 55 attempted murders, 116 rapes, 68 other sexual offences, 119 aggravated burglaries, and 127 drugs offences."

The figures Brown cited are drawn from the Home Office's NDNAD annual report. The most recent numbers say that "200,300 or so" profiles have been retained that would have been removed before the Criminal Justice and Police Act 2001 hit the statute book. That number is estimated from comparing the number of entries in the Police National Computer (PNC) to the number of DNA profiles.

The Home Office then calculates what proportion of the entire NDNAD acquitted and untried suspects represent. This factor is used to estimate that 13,964 offences recorded by the police in 2005/06 were matched to a profile on the database that would not have been retained before 2001. In turn, the number of those supposed matches that would have been murder cases is calculated: 114.

And finally, the Prime Minister informs the public that 114 murderers would "in all probability have got away".