Rally round, you English pedants

There is a tiresome breed of pedant who insists that the term "Union Jack" should be applied to the national flag only when it is flown at sea - from the jackstaff of a ship. Otherwise, they say, it should properly be known as the Union Flag.

But an Admiralty circular of 1902 noted that the two names were interchangeable, and Parliament declared in 1908 that "the Union Jack should be regarded as the national flag". As Nick Groom points out in this vivid, fascinating and carefully researched history of the flag in all its manifestations, Parliament was only confirming what had been recognised since at least 1674. So, pedants, get over it. Groom has pronounced the final word on this subject. Unashamedly calling his book The Union Jack , he confirms the triumph of common usage - and, after more than 300 years, it is about time.

The story of the flag is a complex one. In its present form, combining the crosses of St George, St Andrew and St Patrick, it dates from 1800, when Ireland was formally incorporated into the United Kingdom. Previously, the Union Jack had consisted of just the flags of St George and St Andrew. I, for one, never realised that the earlier UK flag, which dated from the union of the kingdoms of England and Scotland in 1603, had the flag of St George superimposed on that of St Andrew when flown in England, but the flag of St Andrew superimposed on that of St George when flown in Scotland.

The new flag was first flown on April 12, 1606. The emblem of Wales has never appeared in the Union Jack because Wales was "incorporated, united and annexed" to England by two acts of union of 1536 and 1542-43.

But Groom's book traces far more than just the evolution of the Union Jack. It gives the histories of the constituent flags of St George, St Andrew and St Patrick and other symbols of nationhood such as Britannia, John Bull, God Save the King , the three lions of England and the red dragon of Wales.

In telling the story of the national flag, Groom has had to master the intricacies of heraldry, and he leads us confidently through the elaborate byways of that arcane but endlessly intriguing science. There were initially half a dozen different designs prepared for James I by the Earl of Nottingham, any one of which we might have ended up with. One was a quartering of the flags of St George and St Andrew. Another was an impaling (placing them side by side). A third had St Andrew's flag in the top left-hand corner, and a fourth had it in the middle. To complicate matters still further, the Cromwellian Commonwealth abandoned the Union Jack for a much more fussy replacement in which a quartering of the flags of St George and St Andrew and the harp of Ireland was impaled with three leopards and had Cromwell's personal arms of a silver lion on a black shield in the middle. Fortunately, the restoration of King Charles II in 1660 signalled the return of the original Union Jack.

The post-1800 Union Jack came to be seen as the symbol of the British Empire, a shared project in which the English, Scottish and Irish participated equally. It figured on the flags of colonies such as Australia and Canada as a symbol of the link with the mother country. It even appeared in the corner of the original design for the American flag in 1776, but it did not survive into the final version.

In the 19th century, the Union Jack was ubiquitous in popular culture, in painting, poetry and drama. Groom excavates a rich and evocative vein of "Union Jackist" poetry, typified by poet laureate Alfred Austin's "The Flag of England" in which, though writing about the Union Jack, he elides England and Britain. This happened all the time in the heyday of empire.

The use of the flag in Victorian melodrama has eluded Groom's otherwise all-seeing eagle eye. In two plays, The White Slave or the Flag of Freedom (1849) and British Born (1872), there are identical scenes in which the British hero, surrounded by hostile natives, wraps himself in the Union Jack and dares them to fire on him. They lower their rifles in shame and he is saved.

The end of the empire, the process of constitutional devolution and Britain's incorporation into the European Union has triggered something of a crisis of identity for the English. The same has not occurred for the Scots and the Irish as they had always maintained their separate national identities alongside their participation in the wider British Union. The English did not. For them, England and Britain were interchangeable.

However, in the absence of an English national costume and an English national anthem, the desire to express a distinctive English identity took the form of the revival of the flag of St George, a development Groom dates to the 1990s. As he rightly points out, when England won the World Cup in 1966, Wembley Stadium was awash with Union Jacks. In the 2006 World Cup held in Germnay, it was flags of St George that accompanied England's campaign. But the continuing confusion of England with Britain was encapsulated in the songs sung in the German stadiums, which were the British national songs God Save the Queen and Rule Britannia .

Groom tackles head-on the question of the future of the Union Jack, which is a particularly pertinent question because there is a breed of po-faced postcolonialists who have misguidedly suggested that the Union Jack should be abandoned in favour of the flag of St George because it is associated with too many 19th-century imperial atrocities. But this completely overlooks the fact that the flag of St George waved over just as many medieval atrocities, such as the slaughter of the captured French at Agincourt.

Groom enters a robust, positive and wholly persuasive defence of the retention of the Union Jack as the symbol of coherence and unity in a multi-racial society and what has become a federal kingdom. He concludes:

"There could be no better flag to map the ebb and flow of identity and of multiple identities, of nationality... and of plural nationalities... It can be read as a symbolic chart of different lands and different peoples, and of the ways they found to live together." Bravo.

Jeffrey Richards is professor of cultural history, Lancaster University.