IN PICTURES: Inside Winston Churchill's War Rooms

The underground war headquarters were described as 'masses and masses of corridors' needing 'sun ray lamps', according to rare papers...

Above: Winston Churchill seated at his desk in the No 10 Annexe Map Room, May 1945 (Picture: PA/Imperial War Museums).

Winston Churchill's War Rooms were 'masses and masses of corridors' needing 'sun ray lamps', according to rare papers and insights from people who worked in the underground headquarters.

The Imperial War Museums have revealed documents, testimonies and images showing what life was like under Central London to mark the UK release of the film 'Darkest Hour', which recounts the early days of his premiership.

They include a rare surviving example of a letter confirming a typist's appointment, and insights from Churchill's private secretary, Elizabeth Layton, and other secretaries working in the underground bunker.

A letter confirming the appointment of a typist in the War Rooms (Picture: PA/Imperial War Museums).

His private secretary's reminiscences include details of the leader's routines, such as his habit of having breakfast in bed, and remaining there with a secretary and typewriter near his bedside until he got up, sometimes as late as 1pm. She said:

"We of his personal staff were completely devoted to him, even though he was inclined to be impatient and demanding.

"He was somebody who drew our loyalty and our deep respect and affection ... The negative side was only on the surface. Underneath he was a very caring person."

Myra Nora Collyer, a secretary working in the war rooms, remembered the "masses and masses and masses of corridors" and the need for "sun ray lamps" once a week because they were working 12-hour shifts underground.

Margaret Walker, employed as a typist and secretary, recalled:

"He (Churchill) used to wear a siren suit and we used to see this shortish, fattish, tubby man bouncing along in a siren suit."

A siren suit, similar to a boiler suit, was an all-in-one garment which could be easily put on over other clothing and used by people who had to leave their homes for air raid shelters during bombing raids.

Other documents include early plans for the basement headquarters and security passes.

Photo of the original plan for the Cabinet War Rooms (Picture: PA/Imperial War Museums).

The materials have been released to inspire people to visit the Churchill War Rooms, which are featured in 'Darkest Hour' and are open daily, allowing visitors to walk in the footsteps of people who worked there.

Visitors will also be able to see locations which were recreated for the film, including the map room, the cabinet room, Churchill's bedroom and the transatlantic telephone room.