The Kit-Cat Club, By Ophelia Field

In Room 9 of the National Portrait Gallery in London hangs a fine and fascinating series of paintings by Godfrey Kneller. They cluster together in a chummy group, these portly men with amused expressions. They're a strange mix, both in social standing and in presentation; some wear wigs and velvet finery, others caps or turbans and loose shirts; earls and dukes rub comfortable shoulders with those who are merely Esq. Among the names, the casual visitor might recognise the writers Addison and Steele, who founded The Spectator. Otherwise it's a mystery. Who are they, what links them, and why do they look so pleased with themselves?

Ophelia Field has written the definitive history of these men and their influential society, the Kit-Cat Club. The story is as beguiling as the portraits themselves; in her hands these enigmatic oil paintings become flesh and blood again.

In among all the big w(h)igs it might be easy to overlook a humble publisher, Jacob Tonson, a portly figure in a red cap, shown clutching a copy of Paradise Lost. However, Tonson was the club's founder and its camaraderie must owe something to his magnetism and energy. The club's origins sometime in the 1690s are vague, but legend has it that it was named either after the baker Christopher "Kit" Catling, or his eponymous pies, eaten at an unpretentious establishment in Gray's Inn Lane. Two elements of the story – the gourmandising and the egalitarianism – became hallmarks of the society, as Field notes.

An opportunistic publisher, Tonson first conceived of the club as a way of feeding and fostering loyalty in hungry young writers – in Field's words, it was simply "an eccentric publishing rights deal... Tonson wished to forge professional loyalties in the heat of Cat's pie oven, with an eye to longer-term profits." Tonson was a great networker with contacts to the highest in the land. In an era of vicious party politics, it soon became useful to Whig politicians to make the acquaintance of young pamphleteers who could attack Tory policies and boost their own.

Another pivotal early figure was Lord Dorset, who in his youth had roistered with Lord Rochester at the court of Charles II. "Lord Dorset's Boys", Charles Montagu, Matthew Prior and George Stepney, were Dorset's gifted protégés; despite their widely differing social status, they had bonded while enduring the tough regime at Westminster School, where they had slept in a dilapidated former granary. Field's organisation of the complicated story is masterly over the 30-odd year history of the club. Attractive characters such as Prior, the apostate who eventually defected to the Tories, move in and out of the narrative. New members arrive, old ones fade away, while charismatic figures like Addison, Steele and Congreve remain in the foreground.

The Kit-Cats had to steer their party through Queen Anne's tricky reign (she inclined naturally to the Tories), and the crisis on her death when the Whigs wished to ensure the Protestant succession of George I of Hanover. The Kit-Cats' tentacles stretched to Ireland and the continent; in a brilliant final chapter about their influence, Field demonstrates that they functioned as a Cabinet (at times of Tory ascendance, a Shadow Cabinet). Considering the heterogenous nature of the individual members, they maintained a remarkable resolve and unity.

The story isn't just limited to politics, though; the club had cultural objectives too. Addison tried to rid England of Italian opera and encourage a home-grown variety (not one of the Kit-Cats' successes); Congreve and Vanbrugh revitalised the theatre to howls of protest; Blenheim and Castle Howard were Kit-Cat projects. (Marlborough, though much courted by the club, was never a member.) Most important of all was The Spectator, which brilliantly managed never to read like a Whig rag, while nevertheless scoring points off the Tories. The wildly successful paper represented all that was fashionable, new and desirable, and the Tories couldn't help but look stuffy, despite the benign caricature in its pages of Sir Roger de Coverley. Field points out that even today, a great deal of what we conceive of as the "English character" actually derives from the pen of Addison and the pages of The Spectator.

A few women make memorable appearances in these pages; for example Steele's long-suffering wife, Prue, apt to go on a sex-strike when he kept her short of cash, and Mary Wortley Montagu, who was dressed up and paraded before the club aged seven and awarded one of their celebrated "toasts" as a Whig beauty (they continued to toast her for some years, until she became disfigured by smallpox). But this is above all a hugely enjoyable study of male friendship – the subtitle is "Friends Who Imagined a Nation". Kneller's portly gentlemen in their frames have a new reason to smile.