Philip Hensher's novel begins with a dinner party in Sheffield back in 1974, and follows the fortunes of two families, the Glovers and the Sellers, over the ensuing 20 years against the backdrop of a changing social landscape.

Given its scope, it is perhaps not surprising that the novel, Hensher's sixth, occupies so many pages, but he insists it wasn't his intention. "I didn't think it would be quite as big as it is, but if you're covering 20 years of British history and have 10 main characters that's not always possible," he says.

Novels on this scale require mountainous levels of research, but Hensher eschewed such time-consuming methods. "If you do that, you end up putting things in just because they're fashionable, which doesn't necessarily work, so I relied quite a lot on my memories of what life was like."

He admits that writing about the past can be fraught with difficulty. "If you take the '70s, for instance, there's the real '70s and the nostalgic version where everyone watches Top of the Pops and kids are riding around on choppers. I wanted to strip away at this. The big public events that happened are there, like the miners' strike, but they give a flavour to the characters' lives rather than shaping them."

Unlike his previous books such as Pleasured, set around the fall of the Berlin Wall, or The Mulberry Empire, a historical epic dealing with Britain's 19th century Afghan wars, his new book contains echoes of his own past. Hensher moved with his family to Sheffield from London, just as the Sellers family do in the book, and many of the characters are based on people he's known. "Quite often novelists start with something autobiographical, but it's taken me quite a while to develop the technique to the point where I could write about things with the right kind of detachment."

Hensher was nine years old when he moved to Sheffield, where he attended Tapton School, and says it was an obvious place to set his intimate portrait of family life during the Thatcher era.

"It had to be Sheffield because I grew up in the city and it's somewhere I know very well." Although he now lives in London, he regularly visits his parents who still live in the city. "It's changed dramatically," he says. "It's more entrepreneurial than it was, but I think it's lost some of its character, like most other cities."

Hensher, a columnist for The Independent and arts critic for The Spectator, didn't start writing fiction until he was well into his 20s. "I just started writing a novel one day," he says. "But it all came very easily. Once I started it just flowed, I certainly can't write as easily as that now."

The Northern Clemency might provoke comparisons with another epic, Don DeLillo's Underworld, but Hensher says he was more influenced by Russian writers of the 19th century like Tolstoy and Dostoevsky.

"It's ended up being about life in Britain during a certain time, but it's not a manifesto of any kind," he explains. "It's about families and family life and the motives behind why people do what they do. It's also about change and what it does to people."