David Cameron has accused Gordon Brown and John Reid of "tough guy posturing" and trying to play politics with Britain's security.
The Tory leader said Tony Blair was acting in good faith in attempting to tackle terrorism and urged the Chancellor and Home Secretary to follow suit.
He hit out after Mr Brown and Mr Reid signalled their support for an increase in the 28-day period police can question terrorist suspects without charge. The Home Secretary has also argued that the fight against terrorism is being undermined by the Tories' opposition to identity cards.
Mr Cameron said: "The two main contenders for the Labour leadership are vying to outdo each other on how 'tough' they can sound on security and I want to say something directly to Gordon Brown and John Reid - everyone can see what you're up to. There is no shame in seeking the leadership of your party, but to use national security for political ends - that is not leadership. So let's stop the 'tough guy' posturing, let's put the national interest first and let's work together to make our country safer."
In a speech to the International Institute for Strategic Studies in London, he said: "Putting politics before security leads to an approach that is hasty and hysterical - and that can never be in the national interest."
He said his party would take "a lot of persuading" to back moves to extend the limit 28-day limit. "Our liberties are not elastic."
The Tories are also preparing for a policy shift on poverty. The move follows a report by Greg Clark, an adviser to Mr Cameron, who said the party should ditch Winston Churchill's attitude in favour of the liberal ideas of Polly Toynbee, the Guardian columnist.Reuse content