Ministers have been accused of "complacency" for letting armed police numbers fall while gun crime has been soaring.
The drop has been most pronounced in "hotspot" areas which have seen the biggest rises in offences, according to figures obtained by the Tories.
The apparent reductions come despite the Government repeatedly boasting that total police strength is the highest it has ever been.
In Northamptonshire, gun offences more than trebled to 128 between 2002 and 2006, but the number of authorised firearms officers has dipped more than a third to 56 since Labour came to power.
Merseyside saw the number of authorised firearms officers fall 15% between 1997 and 2006, while reported crimes involving firearms rose 62% between 2002 and 2006.
And over the same periods in Avon and Somerset, armed police levels dropped from 165 to 117, as reported gun offences went up 62%.
Overall, the number of authorised firearms officers went down from 6,738 in 1997 to 6,584 in 2006, while the total number of reported firearms offences rose more than 10%.
Shadow home secretary David Davis said the details, disclosed in response to Parliamentary questions, showed ministers were "part of the problem".
"These are yet more statistics betraying the Government's complacent approach to gun crime," he said.
"It is clear that when it comes to tackling the scourge of gun crime and other violent crime, Labour are part of the problem, not the solution."
