In the hour-long programme, the monarch recounts the difficulty of wearing a heavy crown and how uncomfortable it is to travel in a golden carriage.

The trials and tribulations of being head of state have been revealed by the Queen in a BBC documentary that features rare comments from the monarch on the perils of wearing the crown and the pain of travelling in a golden carriage.

In the hour-long programme The Coronation, to be aired on Sunday, the Queen speaks candidly about the moment she was crowned and jokingly says she cannot look down while wearing the Imperial State Crown, which weighs 2lbs 13oz (1.28kg), as her “neck would break”.

She also recounts how she was brought to a standstill when her heavy ceremonial robes ran against the thick carpet pile in Westminster Abbey during her coronation.

The documentary features the monarch in conversation with royal commentator Alastair Bruce and tells the story of the crown jewels and the ceremony of crowning a new monarch.

Speaking with the Imperial State Crown – worn when delivering her speech during the state opening of parliament – in front of her, the Queen said: “Fortunately, my father and I have about the same sort of shaped head. But once you put it on, it stays. I mean, it just remains on.”

She added: “You can’t look down to read the speech, you have to take the speech up. Because if you did your neck would break, it would fall off.

“So there are some disadvantages to crowns, but otherwise they’re quite important things.”

The crown was made for George VI’s coronation in 1937 and is set with 2,868 diamonds, 17 sapphires, 11 emeralds and hundreds of pearls, including four known as Queen Elizabeth I’s earrings. It also features a gemstone known as the Black Prince’s Ruby, believed to have been worn by Henry V at the Battle of Agincourt in 1415.

The Queen joked that Elizabeth’s pearls were “not very happy now”, adding: “I mean, the trouble is that pearls are sort of live things and they need warming.”

The Queen acceded to the throne on 6 February 1952 aged 25 when her father died at Sandringham in Norfolk. Despite the country being in the grip of post-war austerity, a glittering coronation was staged on 2 June the following year at Westminster Abbey.

Her coronation dress was embroidered in silk with pearls, and gold and silver bullion thread. The Queen recounted: “Well, I remember one moment when I was going against the pile of the carpet and I couldn’t move at all … They hadn’t thought of that.”

The Queen also remembered riding in a golden carriage from Buckingham Palace to the abbey, describing the journey as “horrible – it’s only sprung on leather, not very comfortable”.

Looking back on the coronation, she said: “It’s the sort of, I suppose, the beginning of one’s life really as a sovereign.

“It is sort of a pageant of chivalry and old-fashioned way of doing things, really. I’ve seen one coronation and been the recipient in the other, which is pretty remarkable.”

The documentary also features informal footage taken behind the scenes, including son and heir Prince Charles, then aged four, and his younger sister Anne playing underneath the Queen’s long robe.

“Not what they’re meant to do,” the Queen said.

The documentary is part of the Royal Collection Season, a partnership between the BBC and Royal Collection Trust, which also features the four-part television series Art, Passion And Power: The Story Of The Royal Collection.

The Coronation is screened on BBC One at 8pm on Sunday.