David Cameron pledged today to re-establish trust in the system of foreign policy decision-making in the wake of the fiasco of the Government's so-called "dodgy dossier" on Iraq.
The Tory leader said a future Conservative government would have to "think through much more carefully" whether to commit British troops in military interventions overseas.
In a keynote speech to the Chatham House foreign affairs think tank in London, he also announced plans to establish a new cyber threat and assessment centre to guard against attack on the UK's vital computer network.
Mr Cameron said it was "hard to overestimate the damage" caused by the "dodgy dossier" - the second to be published by the Government on Iraq - which included material lifted from the internet, even though it was supposed to be based on intelligence.
"It's made people suspicious of something they should be, frankly, always be able to rely on," he said.
His comments followed the appearance earlier this week of Tony Blair's former communications chief Alastair Campbell before the Iraq Inquiry, which once again turned the spotlight on the dossiers.
Mr Cameron said that if he was prime minister, he alone would decide whether intelligence assessments should be published.
"Political advisers will not be permitted to change intelligence assessments, and any publication of an assessment should only be done by the Joint Intelligence Committee (JIC), with the express clearance and approval of the JIC," he said.
"And we will end the culture of spin by making sure that decisions about national security are taken formally, not on the sofa but round a table, and with all the right people sitting round the table."
In a further apparent swipe at Mr Campbell, he said that he would employ people who would "lift politics up" rather than drag it down.
"If you hire responsible people, people you really trust who want to lift politics up not stoop down to its lowest level, then you have your best guarantee against dodgy dossiers," he said.
Mr Cameron suggested that a Conservative government would be cautious about taking on new overseas military commitments and, if it did, it would take steps to avoid the chaos which followed the invasion of Iraq.
"We've got to think through much more carefully whether Britain should get involved in a foreign conflict, and if so, how to cope with the consequences," he said.
"And then if we do intervene and send troops to fight in a foreign country, there should be a proper reconstruction force ready and waiting to deliver a stabilisation strategy as soon as the fighting stops."
The Conservative leader pointed to the so-called "clickskrieg" cyber attack on Estonia in 2007, which crippled the country's government and banking systems, as an example of the need to strengthen the safeguards in the UK.
"We know that there are hundreds of thousands of cyber-attacks and crimes against British businesses every year. Against government and the public sector, there may be many more," he said.
"I want Britain to be prepared and proactive and ready to deal with all kinds of cyber attacks. So today we're announcing plans for a new cyber threat and assessment centre to provide exactly that."