David Cameron will today contend Labour's bruising election contest dragged it to the "extremes", meaning it poses a "clear threat to the financial security of every family in Britain".
In the opening salvo in what is likely to be a sustained attack on the Opposition when, as expected, Jeremy Corbyn is elected leader, the Prime Minister will paint a a picture of a party "wedded to more spending, more borrowing, and more taxes".
Mr Cameron will today give a speech spelling out his vision for a “smarter state”, renewing an argument that austerity is not just about balancing the books but creating an "opportunity society" at the same time.
"We can spend less and deliver more," he will say, arguing there is a "moral imperative" to "streamline" services to be more "effective" weeks before George Osborne publishes his next spending review.
"When a business uses technology to deliver more for less, it's regarded as a good thing. But when government does it, it's too often just badged as cuts."
But the attack on Labour is most striking. Warning Mr Corbyn, a senior Stop The War Coalition Figure, would put Britain's national security at risk will be a recurring them if elected, the first of many likely onslaughts will focus on the economy. Mr Corbyn's anti-austerity programme has been criticised even by his Labour rivals.
“I have watched with some bewilderment the Labour leadership election of the past few month," Mr Cameron will say.
"Their whole debate seems to ignore what almost every other political party in almost every other country has now grasped. They’re still debating whether the deficit needs to be cut.
“Whoever wins the Labour leadership tomorrow, this is now a party that has completely vacated the intellectual playing field and no longer represents working people. It is arguing at the extremes of the debate, simply wedded to more spending, more borrowing, and more taxes.
“They pose a clear threat to the financial security of every family in Britain. There’s only one party that understands the big question facing our country, and one party that is developing an answer to it – and that’s the modern Conservative Party.”