"You know what they call them on Deeside?'' The wee man in the Glasgow pub thrust his face closer to mine. "The Germans, that's what they call them, the Germans.'' Though I lived for several years on Deeside, about 20 miles from Balmoral, and had never heard any locals refer to the Royal Family as "the Germans,'' I didn't argue. It was that sort of Glasgow pub, and the wee man had already told me about the knife he always carried. Besides, even if he wasn't absolutely right in what he said, he had a point, sort of, anyway.

Kings and queens are symbols of national unity. For royalists they even embody the nation. Yet they have rarely been thoroughgoing members of the nation or nations over which they reign. This is because from at least the early Middle Ages royals have chosen or been required to marry other royals, who have been almost inevitably foreigners.

So, for example, Spain came to be ruled by Habsburgs, who were German, and then by Bourbons, who were French. Elizabeth of England's rival, and sometime brother-in-law, Philip II of Spain, had only one Spanish grandparent, and, being blond, he took after his Flemish (or Belgian) grandfather, and didn't look Spanish at all. Our own Royal Family is no different. It is true that the Queen can trace her descent from the Saxon king Alfred, heroic defender of Wessex against the Danes and also from the 11th-century Scottish king Malcolm Canmore (the Malcolm of Shakespeare's Macbeth); but there have been rivers of foreign blood since. Royalty are among the most successful of immigrants.

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The last monarch to have been as much as half-English by birth and heredity was Queen Anne (1702-14). Her father, James, Duke of York made what was considered a misalliance, marrying a commoner, Anne Hyde, whose father had been a mere lawyer, though as Charles II's chief minister (1660-67) he was created Earl of Clarendon. None of Anne's 17 children lived to adulthood. So, when the poor woman, who had suffered for years from gout and dropsy, died in 1714, it was necessary to import, as her nearest Protestant relation, George, Elector of Hanover. The British monarchy therefore became German. (His family name was Guelph, but they are usually known as the House of Hanover, or the Hanoverians.)

Of course George, a dull man of 54, unable to speak English, and with no desire to learn the language, wasn't 100 per cent German. His grandmother, who is generally, if confusingly, known as Elizabeth of Bohemia, was the daughter of James VI - the King of Scotland who in 1603 became also James I of England - and his Danish wife, Anne. Elizabeth was married to a German prince, Frederick, Elector Palatine of the Rhine, who in 1618 was offered the throne of Bohemia (the modern Czech Republic) and rashly accepted it, thus kicking off the terrible Thirty Years War.

George's line was established, and for the next century and a half their sons and daughters married only other Germans. There were two reasons for this: first, the rule that royals must marry other royals, and there was fortunately an abundance of princes and princesses in the numerous German states; second, the chosen wife or husband must be a Protestant, and this excluded all royals south of the Rhine.

The first two Georges were happy to be German and much preferred Hanover to England. But, despite the marriage requirement, the family was gradually assimilated, as in time immigrants usually are. George II's son, Frederick, Prince of Wales ("Poor Fred'') died as a result of an injury received while playing cricket, which couldn't be more English. Fred's son, George III, declared that he "gloried in the name of Briton'', using a word usually reserved for the chaps who painted themselves with woad in the days of the Roman Empire.

Nevertheless, this king came to be accepted as very English and was known as "Farmer George''. His disreputable sons, despite having no English, Scottish or Welsh blood, except that filtered to them by way of Elizabeth of Bohemia, were all more English (or British) than German in outlook, habits and language; but they still had to take German wives. So Edward, Duke of Kent, married Princess Victoria Mary Louisa, a daughter of the Duke of Saxe-Coburg-Saalfeld. You couldn't get much more German than that. They had a daughter, who in 1837 became Queen Victoria.

Victoria's first language was German (not surprisingly), but she soon learnt to speak English. She married, naturally, a German cousin, Albert. So the family name now became Saxe-Coburg-Gotha. Victoria and Albert corresponded in a mixture of English and German and spoke to each other in either language. But Albert, unlike earlier German royals, tried very hard to identify himself with his new country, and Victoria became more English, or perhaps Scottish, the longer she lived. That qualification is necessary because she preferred Balmoral to her other residences, and was never happier than when among her beloved Highlanders on Deeside. Actually, Albert had chosen to buy the small estate of Balmoral because the landscape reminded him of the romantic scenery around "dear Rosenau,'' his birthplace in Coburg.

Dynastically, Victoria was the most successful of all British monarchs, becoming the grandmother of (royal) Europe. Her eldest daughter married the Crown Prince of Prussia, and their son was Kaiser Wilhelm II - the Kaiser of the 1914-18 war. He liked to believe he was Victoria's favourite grandchild. His one moment of popularity here came when he hurried to the old queen's deathbed, and, arriving at Victoria station, said: "No ceremony. I come as grandson, not emperor.'' The 1914-18 war changed everything. Germany and things German, once admired, were now anathema. Dachshunds were stoned in the streets and George V decided that the family name was now an embarrassment.

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So, in the summer of 1917, shortly after Germany dispatched 23 Gotha bombers to Britain, resulting in the deaths of 76 civilians on the south coast, he changed it to Windsor. (This occasioned one of the Kaiser's few good jokes. "I look forward,'' he said, "to the next performance of the play, The Merry Wives of Saxe-Coburg Gotha''. Well, it's a good joke, as royal jokes go.)

Anti-German feeling drove the First Sea Lord, Prince Louis of Battenburg, from office - though he too was a grandson of Queen Victoria. He also thought it prudent to change his family name, and did so by translating Battenburg into Mountbatten. His son became, eventually, Earl Mountbatten of Burma, and his great-nephew is Prince Philip.

The shock of the Great War made all German associations suspect, while the collapse of the German, Austro-Hungarian, and Russian Empires left the British monarchy suddenly isolated. It was necessary to emphasise its Englishness, or rather its Britishness. (Nevertheless, in Lisbon in 1940 the former Edward VIII, now Duke of Windsor, was reported to have said he didn't care who won that new war, adding: "I'm half a German anyway.'' But this story may not be true.)

The rule about princes marrying only royals was relaxed. So two sons of George V, the Duke of York and the Duke of Gloucester, married British women. York's wife was Lady Elizabeth Bowes-Lyon, daughter of the Earl of Strathmore. After his brother's abdication, he became George VI and she Queen Elizabeth, known to most people later as the Queen Mother. Being the daughter of a Scottish aristocrat, she regarded herself as a Scot, though her mother was English and she was herself born in England.

Consequently, our Queen, being her daughter, is more British, or Anglo-Scottish than any reigning monarch for centuries. So completely has the German heritage been sloughed off - despite what my friend in that Glasgow pub thinks - that on her state visit to Germany this week, the Queen made her speeches in English, even though when she visits France she delivers them in French.

It seems that her German isn't good enough. It would, of course, have been highly inappropriate for her, aged 13 in 1939 and the heir to the throne, to have been taught German. In any case her mother would not have permitted it. She was anti-German, two much-loved brothers having been killed in the 1914-18 war.

Prince Philip, on the other hand, speaks good German and has close German relatives. Naturalised British, and known as Lieutenant Philip Mountbatten at the time of his marriage to the Princess Elizabeth in 1947, his heredity is complicated. A descendant of Queen Victoria (like almost every European royal, even King Juan Carlos of Spain), he is a member of the Greek Royal Family who, however, are not Greek but Danish, a son of King Christian IX of Denmark having been elected King of Greece, as George I, in 1863. (Christian's sister Alexandra, incidentally, married Queen Victoria's eldest son, the future Edward VII.)

Subsequently, the Greek royals usually took German wives or married their daughters to German princes, for the old reason: that there were lots of German royals about. Prince Philip is connected to almost every royal and imperial family, being for instance also a descendant of the Romanovs, the Tsars of All the Russias. But nobody can doubt that, ever since he served in the Royal Navy, he has also been wholeheartedly British.

Royal exclusivity is now dead, since members of the Royal Family are no longer required to restrict their choice of wife or husband to members of other royal families. To do so would be to emphasise their difference from the rest of us, and since the reign of George V, it has been the policy of our Royal Family to present themselves as being in tune with Middle Britain. The aim is to be like us, only royal. So arranged marriages to foreigners are out. Instead, the young royals may now marry for love, and do so, even if the evidence suggests that this doesn't necessarily make for happy or enduring relationships. But what it does mean is that the generation of royals now in their twenties or teens are more British, by birth and heredity, than any have been for centuries.

They have the Queen and Prince Philip as grandparents of course, but on the other side of their genealogical table, you find names like Spencer, Phillips, Ferguson, Rhys-Jones. Only one of these names, Spencer, is aristocratic, and the Spencers themselves are very English, having first come to prominence as Midlands sheep-farmers in the 16th century.

Most of the other grandparents of the young royals are solidly, comfortably middle-class and British, without foreign connections. When he eventually succeeds to the throne, Prince William will be the most English monarch since Queen Anne, and the most English king since Edward VI, Henry VIII's son by his marriage to Jane Seymour, daughter of a West Country landowner.

And through his great-grandmother, the late Queen Mother, he also has Scottish blood, less remote than that of the Stuart kings. There remains of course a difference. Not many of us can trace back our ancestry for more than a thousand years; and though the young royals will all have some bloodlines that get lost quite early in the mists of time - in this respect being just like the rest of us - on their royal side they go back beyond Stuarts and Tudors to Plantagenets, Normans, the MacMalcolm kings of Scotland and the Saxon kings of Wessex and England - all that before they even consider their connections with European royalty. Whereas we know little or nothing about our forebears, Queen Victoria could declare that she could never forgive her predecessor Elizabeth I for "her cruelty to my ancestress, poor Mary Queen of Scots".

She said that in English of course, for the little, German Princess became a very British queen. The German origins of the Royal Family have long been irrelevant. They are as British as the rest of us, many of whom, anyway, have foreign immigrant strains in our pedigree.

That chap in the Glasgow pub was talking nonsense. I knew he was; but mindful of that knife, I thought it wiser to keep quiet.