Britain's new National Security Strategy is expected to name terrorism and cyber-attacks on vital computer networks as the biggest threats to the UK in the immediate future.
The strategy, to be announced by David Cameron in a written statement to MPs, has been drawn up by the Prime Minister's new National Security Council as part of an assessment of Britain's defence needs which he ordered in May.
It will set the scene for Tuesday's Strategic Defence and Security Review (SDSR), which will sketch out the shape of Britain's future armed forces and explain what equipment and manpower will have to be sacrificed to achieve the 7%-8% savings demanded by the Treasury.
A leaked draft of the national security document suggested that military conflict with another state will come only fourth in a list of potential threats to the UK, behind terror outrages by groups like al Qaida, cyber-attacks and natural disasters.
The launch comes just days after the head of the Government's GCHQ eavesdropping centre, Iain Lobban, warned of the very real danger of cyber-terrorism directed at the UK's critical computer infrastructure.
He said that there were 20,000 malicious emails on Government networks every month, and significant disruption had been caused to official systems by electronic "worms". Cyberspace had "lowered the bar for entry to the espionage game for states and criminals."
Reports suggest that cyber-warfare could receive a £500 million boost in Tuesday's SDSR.
The expected focus of the document on terrorism will underpin moves towards mobile military units, intelligence-gathering and special forces and away from the tank brigades and jet fighters which dominated defence thinking in the Cold War.
This strategic shift is certain to be reflected in the SDSR, which is expected to pave the way for manpower cuts in all three services, the closure of RAF bases and the withdrawal of Army tanks and RAF jets.
A personal intervention by Mr Cameron spared the MoD the 10%-20% cuts demanded by the Treasury, and a £5 billion project to build two new aircraft carriers for the Royal Navy will go ahead.