The Lion and the Unicorn, by Richard Aldous

Victoria's twin peaks

In the gentlemanly club that is (or used to be) the British House of Commons, relations between opponents are normally quite civil. Behind the ritual abuse they are frequently good friends. Your real enemies, as Harold Macmillan warned a young MP, are on your own side.

Gladstone and Disraeli were a towering exception to this rule. Gladstone thought Disraeli an unprincipled adventurer, "the grand corrup- ter" of British politics, whose "mischievous and ruinous misdeeds" flouted "every principle of morality". Disraeli thought Gladstone an unscrupulous religious maniac: an "extraordinary mixture of envy, vindictiveness, hypocrisy and superstition - never a gentleman". They met socially as rarely as possible, and never alone. Gladstone conspicuously failed to attend Disraeli's funeral, and had the greatest difficulty composing a suitable tribute.

In fact, they did start out on the same side. Gladstone, the earnest evangelical, was seen as "the rising hope of those stern unbending Tories". Young Benjamin D'Israeli, Jewish dandy and Byronic novelist, was a much more unlikely Tory. Yet it was Disraeli who stuck with the Tories, playing a leading (if opportunist) part in driving the Peelites out of the party following Peel's U-turn in abolishing the Corn Laws in 1846, while Gladstone metamorphosed into a stern unbending Liberal.

As so often in politics, it was not their views that made them rivals but personality and circumstance that drove them to opposite positions. Disraeli tried several times to draw Gladstone back to the Tories - not because he liked him, but because the Tories needed him if they were ever to form more than an occasional minority government whenever the dominant Whig-Peelite coalition fell apart. Throughout the 1850s and 1860s, Disraeli enjoyed only three brief spells as Chancellor, scarcely interrupting Gladstone's magisterial reign of more than nine years at the Treasury under Aberdeen, Palmerston and Russell.

For years they were the heirs apparent of their respective parties. By the time they both reached the leadership, Gladstone was nearly 60 and Disraeli 64. Disraeli briefly headed another minority Tory government ("I have climbed to the top of the greasy pole") before Gladstone convincingly won the 1868 election and formed his first, longest and best administration until 1874.

When Tenniel, illustrating Through the Looking Glass, drew the two rivals as Lewis Carroll's Lion and Unicorn in 1871, it was significantly the Lion (Gladstone) who "beat the Unicorn all round the town". For most of their careers, this accurately reflected the balance of their contest.

Yet they were never less than equals. Disraeli was the one man who could match and often out-smart Gladstone in the Commons. He got his chance to form a majority government in 1874, but by then he was over 70, in failing health, and soon forced to lead from the House of Lords. In this final period their mutual antagonism reached its apogee - fanned by the violent partisanship of Queen Victoria, who loathed Gladstone as much as she adored Disraeli.

Richard Aldous has astutely spotted that no one has previously written up this 50-year vendetta in its own right. Biographers have written about one hero or the other, while other historians have painted the bigger picture or analysed specific crises. Aldous's method is selective and very clever. Beginning each chapter with a vivid, almost novelistic, snapshot, he skilfully traces the ups and downs of their relationship - Gladstone triumphant one minute, the next moment the situation dramatically reversed - without trivialising the scale and importance of the events. The result is a hugely enjoyable joint biography. There really were giants in those days.

John Campbell's 'If Love Were All' is published by Jonathan Cape