Whitehall is throwing is doors open to the public this weekend.

As part of the London Open House weekend important buildings and famous Westminster landmarks usually closed to the public are revealing their secrets.

To celebrate architecture and design, Westminster Hall and the radical Portcullis House will drop their usual access restrictions.

The two buildings are a striking contrast; Westminster Hall is one of the finest and largest medieval halls in Europe dating back to 1097. Portcullis House has won architectural awards but was built only in 2001.

Also opening their doors will be the Foreign Office and the Department for Culture Media and Sport.

"The event has been a huge success in the past and we're very pleased to be taking part," said a DCMS spokesman.

The Office of the Deputy Prime Minister in the grade one listed Old Admiralty building at 26 Whitehall is open after extensive renovations.

Swelling the ranks are the Scottish Office and the Treasury which is just ending a multi-million pound refit.

The Government Art Collection will be on display and offers a behind-the-scenes tour.

The former Liberal Party HQ from 1964 to 1970 in Smith Square, designed by Edwin Lutyens, is also taking part in the event.

And in Neasden, the Underground 1940s bunker used during World War II by Winston Churchill and the Cabinet is open.

To mark the event a CD of poetry has been produced and it includes Roger Robinson's reflections on the Foreign Office.

The GLA's riverside City Hall, designed by Foster and Partners, is also among the buildings taking part and all of the London boroughs have helped organise the event.

The annual weekend has more than 500 buildings open and includes everything from government buildings to City banks, from art deco cinemas to the latest in architect designed residences.

Demand is expected to be high; over 350,000 visits to buildings were made last year.