Book review: Comic cuts and acid drops from the vinegar merchant

With characteristic chutzpah, Andrew Roberts dedicates his massive biography of Robert Cecil, 3rd Marquess of Salisbury, to another "thrice- elected illiberal Tory" - Margaret Thatcher. Yet compared to the Iron Lady, "the Buffalo," as contemporaries nicknamed Salisbury, was a political primitive. He was the most thick-skinned, short-sighted and ill-tempered of late-Victorian reactionaries. Not only did he block progress in every form. He recommended hanging Irish priests, branding Boer rebels and poisoning "influential constituents". The best that could be said for democracy, he thought, was that English voters would not "elect a black man". In short, Lord Salisbury was a blue-blooded redneck.

Despite his obscurantist prejudices and his rebarbative personality, however, the 3rd Marquess was witty, sophisticated and oddly endearing. He was a coruscating writer and an inspired phrase-maker - though it was Lord Randolph Churchill not, as Roberts says, Salisbury who dubbed Gladstone "an old man in a hurry". Unlike most MPs, he spoke with devastating pungency.

Disraeli, whom he called "the grain of dirt" clogging the political machine, famously described him as "a great master of jibes, and flouts, and jeers". John Morley noted that Salisbury could hardly make a speech without some "blazing indiscretion", as when he said that Irishmen were no more fitted for self-rule than Hottentots.

Precisely because he was the Tory id, expressing gut Conservative feelings, Salisbury dominated the party, and thus the country, between 1885 and 1902. Yet this bearish figure was severely handicapped as a leader. He was neurotically shy, once travelling an extra stop by train to avoid an official reception. He was also subject to black depressions, which were perhaps the psychological origin of his political pessimism. His "nerve storms" even invaded his dreams; on one occasion, he was discovered sleepwalking in front of an open window preparing to repulse a "revolutionary mob".

Here then is a marvellous subject for a biography. Salisbury has been neglected in favour of Gladstone and Disraeli, neither of whom served as premier for as long as he did. And Roberts has done Salisbury proud. Based on comprehensive research, this is an outstanding achievement: fluent, weighty in the Victorian mode, sympathetic but not uncritical, often hilarious. Roberts even trumps Peter Sellers's spoof "Lord Badminton's Memoirs" with a story about Lady Salisbury mixing all her family's half-used medicines in a jug with an equal measure of port and administering the resultant concoction to elderly tenants on the Hatfield estate.

With his unbridled cynicism and snobbery, Lord Salisbury is also a great comic character. He denounces Gladstone's abolition of paper duties, "taxes on knowledge", because newspapers do not contain any knowledge. He won't take an umbrella to the Athenaeum since he doesn't trust the bishops not to steal it. He rejoices when Sultan Abdul Hamid awards his wife the Turkish Order of Chastity (Third Class).

Although often sounding like Lady Bracknell, Salisbury emulated Lord Burghley, his ruthless ancestor and Queen Elizabeth's chief minister. At Eton in the early 1840s, where he was mercilessly bullied (which did not stop him sending his sons there), he learned to despise the base many. At Oxford he imbibed High Tory, Tractarian bigotry, which gave him a sardonic disdain for earthly endeavours and most heavenly ones. Evangelicalism, he observed, had no appeal to "the higher class of intellects" though it was popular with "children, with women, and with half-educated men". As a young journalist and politician, he became a ferocious controversialist. Punch called him a "vinegar merchant".

Salisbury advanced partly by attacking Gladstone: the Grand Old Man (GOM) was known at Hatfield as "God's Only Mistake". Still more effective were his assaults on the Conservative chief, Disraeli. According to Salisbury, Dizzy reached the "delirium tremens stage of treachery" by trying to extend the franchise, which would simply produce parliaments full of "tradesmen trying to secrete gentility".

Salisbury was appalled by the 1867 Reform Bill, leading opposition to this "leap in the dark". By 1878, though, there was a rapprochement. Salisbury became Foreign Secretary, helping to bring back "peace with honour" (plus Cyprus) from the Congress of Berlin.

As Disraeli's successor, Salisbury held power by opposing Home Rule, thus splitting the Liberals. However, apart from coercing Ireland and expanding the empire, he achieved almost nothing - because he thought governments could and should do nothing. The point of a Tory government was "to delay changes till they became harmless". And when the cabinet was warned that a new bill would lead to endless time-wasting, Salisbury asked: "Isn't that just what we want?"

Salisbury was a paradox, the highbrow champion of idea-less Conservatism. Whatever was, he reckoned, was right. So he favoured patronage and practised nepotism, prompting the expression "Bob's your uncle". He disliked working- class education, and damned graduated income tax as "the most revolutionary of all schemes". "The people" as an authority had no existence. Socialism was legalised theft. The Lords (a "Paradise of Bores") should decide if the Commons expressed the national will.

Although sceptical about evolution, Salisbury did believe in the survival of the fittest nation. Ethics had no place in foreign policy (not even over opium or slave trading) except when Britain's interest lay in appealing to principle. Good government flourished in secret. Salisbury doctored records, hid state matters from officials, and deceived his ministers about the extent of his belligerence towards the Boers. When the editor of The Times asked for the names of new cabinet members, Salisbury replied: "What is the object of announcing a cabinet?"

Although this is essentially a political biography, it is rich in personal detail. Salisbury tricycles around Hatfield with a footman standing behind him, allows his grandchildren to rootle through his beard, wishes he were a cat so that he need not change his coat, throws cushions at sparking electric lights, murmurs "Bulgaria" when he misses a shot at billiards. Seldom has such an important study been such splendid entertainment.