IT ALL turns on Ferdinand Mount, the political columnist who once ran Baroness Thatcher’s policy unit and became a distinguished editor of The Times Literary Supplement. He is the 3rd baronet in the Mount line but does not use the title.

If one wants to discover David Cameron’s genealogy, one has to look up the entry under Mount in Burke’s Peerage and Baronetage; at the foot of the entry appears David Cameron’s name. His mother was the daughter of the 2nd Baronet Mount, who had no male heirs, so she is Ferdy’s first cousin. David Cameron is, therefore, Ferdy’s first cousin once removed. The Mount family, the forebears both of Ferdy and David, married an heiress of the Talbot family in the mid-19th century, before they received their baronetcy. There is a cross-reference to the Talbot entry, which comes under the Earl of Shrewsbury and Waterford.

The 22nd Earl of Shrewsbury is now the Premier Earl of England and Ireland; his original title was created in 1442 for John Talbot, the heroic general who lost his life at Castillon in the final battle of the Hundred Years War. Two of his sons were killed with him, one legitimate, the other a bastard. The French honoured his courage, calling him “the English Achilles”.

John Talbot was a great national hero of the 15th century, second only to Henry V. He was nearly 80 when he fell in battle. They brought his heart home and buried it at Whitchurch in Shropshire under a great Gothic canopy.

In terms of English history, the Talbots are one of the great families, like the Cecils or the Churchills, only much older. Perhaps the Howards are the closest parallel. The Talbots are an 11th-century family. The Cecils are 16th century and the Churchills, like the Foxes, are 17th century.

In the old Dictionary of National Biography there are 20 entries for members of the Talbot family. The most eccentric is Mary Anne Talbot, the “British Amazon”, who joined the Royal Navy as a transvestite, was wounded, fought as a powder monkey in the battle of “The Glorious First of June”, 1794, and subsequently appeared on the stage in Babes in the Wood. She claimed to be an illegitimate daughter of the 1st Earl of Talbot, yet another family earldom.

The more respectable Talbots, apart from their national hero, produced countless earls, two dukes, though one was only a Jacobite duke, a First Minister, one of Sir Robert Walpole’s Lord Chancellors, a Bishop of Durham, a Roman Catholic Archbishop of Dublin, another medieval Archbishop of Dublin, the great building heiress Bess of Hardwick, and William Fox-Talbot, who invented photography. They married many interesting people, including William Herbert, who was Shakespeare’s patron. Through the Talbots of Malahide, they are connected to James Boswell.

David Cameron aims to become Prime Minister; no one was called Prime Minister before Robert Walpole, but Cameron does have a family forebear who was First Minister. Charles Talbot, the 12th earl and the first and only Duke of Shrewsbury, was born in 1660. He was the first child after the Restoration to be christened with Charles II as his godfather.

When he was only seven a scandalous tragedy happened in the family. His mother was having an affair with George Villiers, the 2nd Duke of Buckingham, a thoroughly contemptible man, even by the standards of the Restoration Court. His father, the 11th Earl, challenged Buckingham to a duel. Buckingham wounded him fatally. The countess is said to have watched the duel, disguised as a page in Buckingham’s retinue. Immediately after the duel contemporary rumours state that she and Buckingham made love; he was still wearing the shirt stained with her husband’s blood. Not an ideal start in life for her son.

Shrewsbury had the knack of holding power at crucial moments in a revolutionary situation. He was the only Secretary of State, and therefore was First Minister, in the first administration appointed by William III in 1689, immediately after the Glorious Revolution. He had been a leading figure in inviting William to invade England, went to Holland to join him, helped to finance the invasion with a loan of £12,000, and even went to console James II and persuade him to abdicate.

Shrewsbury was First Minister again in the later 1690s, when William spent a long time outside England. Early in the reign of Queen Anne he became disgusted with politics and spent some years on the Continent, but he came back and was appointed First Minister by Queen Anne on her death bed. He was therefore First Minister immediately after the accession of William III, again when Queen Anne died and on the arrival of King George I.

How did he do it? Exactly as David Cameron proposes to do it. By charm and moderation. Of his charm and handsome appearance, there are many contemporary accounts. William III himself called Shrewsbury “the king of hearts”, the curmudgeonly Dean Swift said that he was “the finest gentleman we have” and at another time “the favourite of the nation”. Bishop Burnet, whom I always like to quote, wrote that he had “a sweetness of temper that charmed all who knew him”.

Women loved him. He was a political moderate. He was decisive when the revolutionary situation required it, but was one of those politicians who stand above parties, and are seen as relatively non-partisan. According to one of his early biographers: “King William used to say that the Duke of Shrewsbury was the only man of whom the Whigs and Tories both spoke well.”

In his career Shrewsbury helped to make a Whig settlement of our constitution, but for Tory reasons. David Cameron is a Tory with a liberal streak; it is the same combination — it seems to run in the family. The duke, of course, was even younger; he became First Minister at the age of 28.

Times Recommends

• In the real world, the public sector must pay
• Playing politics in a land of double Dutch
• Be like the plinth people: not set in stone