No average superhero

I have always been of the opinion," said Disraeli, "that there cannot be too many Rothschilds." Kenneth Rose's beautifully written, witty and subtle book explains why. From the beginning of the family history, swiftly but sharply sketched here, to the present, there is not a dull page or a boring character. And the central subject, the late Lord Rothschild, is such a spectacular figure that we hardly need, though we greatly enjoy, the supporting cast.

Scientist and FRS, jazz pianist taught by Teddy Wilson, head of worldwide research for Shell, scholarly collector of 18th-century books and of gold and silver objects, outstandingly successful first head of the Government's Cabinet Office think tank, Labour supporter, friend of the Shah, first-class cricketer, bomb disposal man with a George Medal, 1930s Bugatti-driving playboy who loaded the Braques he bought in the back, MI5 man and scientific farmer; Dizzy would certainly have put him in a novel.

Kenneth Rose, who stands very high in the first division of biographers, has deployed his beautiful prose to paint a witty, subtle and sympathetic portrait. But, like a good painter, he gives us more than just a likeness of the sitter. Disraeli again: "Read no history; nothing but biography, for that is life without theory." Rose does not push theory down our throats, but he does use Rothschild's life to illustrate some big themes.

His first is a discussion of that flowering of positive, optimistic, practical, intellectual endeavour which we associate with the names of great scientists, rationalists and social reformers in the first half of the 20th century, who carried on the best traditions of the 19th. Rothschild was part of a world, for him, centered on Cambridge, inhabited by scientists such as Thomson, Dirac, Crick and Brenner, by Maynard Keynes, by Russell and by many others.

This was a culture which believed that no human problem was insoluble by human intelligence, and that humane planning led by enlightened people could establish a society fairer and more moral than that thrown up by the accidents of history and the market. lt believed in planning and was optimistic, and was therefore of the Left, but it was often almost ideology-free (as in Rothschild's case), believing, like Harold Macmillan in his contemporary book The Middle Way - or, perhaps, like our present Prime Minister - that all intelligent people of good will would ultimately agree. Rothschild made a success of the think tank by applying this approach in the over-cynical and super-sophisticated world of Whitehall; if it was naive, it was often more productive than its opposite.

Such rationalism and optimism was a positive flowering of the 20th century. But the two terrible monsters of that dreadful century, Fascism and Communism, in different ways provide the background to other themes which Rose explores.

The English Rothschilds before the Second World War were among the most assimilated of all great Jewish families. Rothschild respected Jewish traditions (his first wife - like the second, a gentile - converted so that their children would be Jewish). But he was liable to say: "obviously I do not eat pork - just get me a ham sandwich"; and though in the 1930s he was one of the first to make the plight of Jewish refugees from Germany into headline news, he was no Zionist.

The Holocaust changed everything. Before Hitler, perhaps, it was possible for a Rothschild to think of himself as a part of a dynasty no different from that of "my cousin Rosebery" or from others with relatively new money like the Cavendishes or the Cecils. But when, Rothschild or not, your elderly aunt has been beaten to death with meat hooks on a German railway station because she was a Jew, you know it is not so. Rose explores the subject of Rothschild's changing relationship to his Jewishness with sensitivity and understanding.

And then the other monster, Communism. Some will look to this book for new revelations about Blunt, Burgess, Wright, spies and spycatchers. To their probable disappointment, what they will find is the truth, carefully grounded in evidence. Yes, Rothschild was a friend and admirer of Blunt's intellect, as were many. Yes, he knew Burgess, who at one time lived in a flat which Rothschild had rented.

No, he was never a member of the Communist Party. No, his loyalty was never for a second doubted by those best able to know, as opposed to gossip writers and Dale Campbell-Savours MP.