The non-descript property at 24 Wormald Street, Symonston has been revealed as central to "Plan Mercator", aiming to maintain "continuity of government" in an attack, and whisking the prime minister, governor-general, senior ministers and top advisers to safety.

Building owners Stavro Dascarolis and Jim Sarris, of Westtech Holdings, are selling the property 11 years after it was built. It is leased by the Attorney-General's Department until 2027.

Real estate agents have advertised it as a "long-term, passive investment" with about $2 million per annum in rent to be paid by the federal government.

The owners would not comment on the building or sale, while the Home Affairs Department would not confirm whether the building played a role under Plan Mercator, saying it would not discuss security matters.

The Attorney-General’s Department said only it was "used for departmental activities", and the building's real estate ad described it as a "high quality, purpose-built data centre/office facility" with 4720 square metres across three levels.

A title document shows a compliance certificate was issued in September after a registrar's dealing to add or alter a restriction was lodged with the ACT government.

The federal government built the top-secret communications facility in the North Symonston industrial estate for $36 million, without publicity or any public inquiry by a parliamentary committee.

An embarrassing disclosure in 2008 through information scattered across government websites revealed the building supported critical communication systems that would operate in the event of a terrorist attack in Canberra.

A job advertisement on the Attorney-General's Department website for a "top secret" classified position in the Secure Services Branch showed the Symonston facility was responsible for providing "communications support for the key functions of executive government following an activation of Plan Mercator".

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''.

One part of Plan Mercator is keeping communications infrastructure operating even if central government agencies in the Parliamentary Triangle and at Russell were destroyed or disabled.

Planning for the facility at Symonston appears to have started in mid-2004.

That year the ACT Planning and Land Authority approved lease and development conditions that included possible use of the site for a "communications facility", "defence installation" or "scientific research establishment".

In November 2005 the authority approved a development application by Mr Sarris for a project at 24 Wormald Street described as a "scientific research building".

Amendments to the plans were later approved in 2006, 2007 and 2008. Construction started on the building in December 2006 and was completed in December 2007.