The peers will head a panel of 17 experts brought together by left-wing think-tank the Institute of Public Policy Research (IPPR).

Over the next 18 months the commission will look at issues surrounding terrorism and other security threats, and make specific policy recommendations.

It will also look beyond Britain's borders to security situations in Iraq and elsewhere.

Lord Robertson, who as George Robertson served as Defence Secretary, and Lord Ashdown, who acted as a UN High Representative to Bosnia, will chair the first meeting.

As well as carrying out a detailed assessment of the threats it will also seek to "identify the values and interests that should shape British security policy over the next decade and beyond".

Director of human rights group Liberty, Shami Chakrabarti, is one of the 15 other commissioners appointed by the IPPR.

Lord Robertson said: "The threats to our national security today are complex and diverse. Issues of state failure, organised crime, terrorism, nuclear proliferation, and energy security have combined to provide a new strategic context.

"While the challenges are real however, there is much we can and should do to meet them more effectively. This commission, and the wide range of expertise it draws upon, will provide a unique opportunity to examine Britain's long-term security needs."

Other commissioners include former US Senator Tom Daschle, former British Ambassador to the United Nations Sir Jeremy Greenstock, former security and intelligence co-ordinator in the Cabinet Office Sir David Omand and Lord Guthrie, the former Chief of the Defence Staff.