WHEN THE QUEEN was crowned, Britain ruled an empire that covered a quarter of the globe. Fifty years later, the largest empire the world has ever seen is “one with Nineveh and Tyre”. What Kipling, the poet of Empire, did not foresee is that not only has this imperial order vanished almost overnight; but it has disappeared entirely from public memory. The British Empire is now a black hole in history, and few dare look in its depths.

Is it shame, guilt, post-colonial exhaustion or plain ignorance that has obliterated the memory of an empire that lasted 500 years and changed the face of the world? Probably all of these. But no one in Britain today can understand what has shaped our multiracial society, what links this country to the Commonwealth and what has made English the tongue of more nations than any other unless they understand the Empire. And nothing seems set to foster this understanding and stimulate overdue debate more effectively than the new British Empire & Commonwealth Museum in Bristol, to be officially opened by the Princess Royal on Monday.

This magnificent assembly of the pictures, words, films, artefacts, pomp and ethos of the Empire is housed, appropriately, in one of the main gateways to imperial trade and commerce — Brunel’s splendid castellated station at Temple Meads, the first main railway terminus in Britain. Rescued from 30 years of dereliction by energetic fund-raising and skilfully restored, the museum has been transformed into an array of 24 themed rooms, beginning with John Cabot’s voyage to Newfoundland, passing through the Canadian fur trade, early Caribbean tobacco plantations, sugar cane and slavery, the South Pacific, India in all its squalor, vastness and glory, the high Victorian panoply of pomp and plumage and on to the 20th century, when white settlers were still leaving for Australia and the Rhodesias, missionaries were serving as dedicated teachers and nurses, and British civil service bureaucracy was planting its pattern across the world.

The museum’s historians faced a tough start: there were no government funds, no documents, collections or early artefacts to hand and no settled historical assessment. They began by seeking out as many living witnesses as possible — those administrators, businessmen, missionaries, emigrants and colonial subjects who had kept the wheels of empire turning and who could record their poignant memories — sometimes triumphant, sometimes bitter — on film. Their eyewitness tales are among the most illuminating in the museum.

Wisely, the museum presents British rule as it was and as it was seen at the time — from all sides. There is no assumed guilt, no apology, no post-colonial hindsights — and, equally, no triumphalism. Sometimes, as Dr Gareth Griffiths, the director, says, “We have put different and even contradictory accounts of the same incident side by side”.

Terminology has also been scrupulous. The Indian Mutiny has been known by that term to generations of British. The Indians now call it the First War of Independence. The museum calls it “the great rebellion of 1857”. And while maps may show Pax Britannica, with pink all over the globe, the commentary notes that “mostly this peace came only after a bloody war of conquest”.

India, of course, is central to the exhibition. The photographs tell the stories — the ayahs, the railways, the tiffin and the regiments. So do the models of those magnificent Indian steam trains, the huge oil painting of the Great Delhi Durbar of 1903 (effectively paralleled by a jerky old film of the same event), the commentaries and the statistics. Upstairs, in a spacious area for special exhibitions and temporary displays, the museum has assembled an impressive collection of pioneering photographs of India from 1850 until 1900, illuminating the daily life of the Raj.

Surprising statistics are dotted around the displays: some 300,000 white servants and prisoners were shipped out to work in the 17th-century tobacco colonies before sugar replaced the failed crops and slaves were imported. More than two million Indians fought with British forces in the Second World War. Between 1815 and 1914 20 million Britons emigrated to the United States and the colonies — which sought, in advertisements, “hardworking, pious and sober” citizens. Scots were favoured; Irish positively discouraged from coming.

It is the little things of daily life that bring the museum alive: the chest of drawers an immigrant might take, complete with passport, knick-knacks and shipping brochures inside; the china vases and porcelain that accompanied the emigrants and Empire-builders to remote settlements; the manacles, whips and chains used for shackling and punishing slaves; the furniture and decorations of colonial houses as well as the quarters for natives; the paraphernalia that fuelled the vicious opium wars with China.

The Empire shaped the thinking and fate of the ruled more than the rulers realised. There was the resentment, hatred and rebellion, vividly illustrated in the section on law and order. There was also the learning, the self-improvement and the opportunity. And there was migration within the Empire. Millions of Indians went all over the world — not just to die in the trenches of the First World War, but as labour to East and South Africa, traders to the South Pacific and students to Britain itself. Griffiths says that most British people now think of the Empire in media-driven images “which can be summed up as ‘Carry on up the Khyber’ ”.

As the Bristol museum shows, it was far, far more than that.

• The British Empire & Commonwealth Museum, Station Approach, Temple Meads, Bristol (0117-925 4980), is open every day from 10am to 5pm