The Federal Government has extensively revised its top secret contingency planning for a possible terrorist attack on Canberra and is considering the construction of new, highly secure, facilities for ministers to use in the event of a national emergency.

The Attorney-General's Department has confirmed that the highly classified ''continuity of government plan'', codenamed Plan Mercator, has been ''rewritten and reformatted'' to allow more flexible responses to a national crisis.

First developed by the former Howard government in the aftermath of the September 2001 terrorist attacks in the United States, Plan Mercator would be activated in the event of a large-scale terrorist attack in Canberra.

The plan aims ''to minimise the impact of a national security emergency on critical government operations and provide for the rapid resumption of 'near normal' government business under alternate arrangements until normal operations can be resumed''.

Plan Mercator provides for the evacuation of the governor-general, the prime minister, senior ministers and key advisers in the event of a major terrorist attack on, or threat against, Parliament House or central Canberra. A key aspect of the plan is arrangements to ensure the effective functioning of cabinet and the federal executive council in a national emergency.

A critical part of the plan is the maintenance of communications infrastructure, capable of operating even if central government agencies in the Parliamentary Triangle and at Russell Hill were destroyed or disabled.

According to the Attorney-General's Department, the revised plan ''provides a more flexible approach to potential activation and offers more response options''.

In June this year The Canberra Times reported that the new $36million Attorney-General's Department communications facility in the North Symonston industrial estate would play a key role in implementing Plan Mercator. The facility's critical role in supporting emergency government communications was inadvertently disclosed in a departmental employment advertisement.

The most recent annual report of the Australian Federal Police says that the AFP would play ''a key role in Plan Mercator a whole-of-government business continuity plan''.

Further revision of the plan is likely as a consequence of Prime Minister Kevin Rudd's decision to consider a recommendation made by former Defence Department secretary Ric Smith for the establishment of a new national crisis coordination centre to support government decision-making during crises.