Philip Hensher has many talents, but providing instant gratification is not one of them. As with his previous books, heft matters. Heft in size, but also in subject, reach and ambition. There are no quick returns in his fiction, and you need commitment and stamina to persevere. But the rewards are ample.

The scope of The Friendly Ones is wide, spanning modern Britain and the Indian subcontinent, immigration, and religious fundamentalism, family dissolution and the nature of love. Set in Sheffield, which is Hensher’s home beat, it is told from the perspective of two families, the general becoming particular as we follow them. So particular, in fact, that at first, Hensher risks losing his reader’s attention.

The cast, for a start, is large. Divided into two parts - The Little Spinsters and The Friendly Ones - the first half of the novel focuses mainly on the Spinster family: a doctrinaire doctor who, as his wife is dying of cancer, tells her he wants a divorce. They have four vertically challenged children, Blossom, Leo, Hugh and Lavinia. Part two gives Dr Spinster’s neighbours their turn. They are Sharif, a professor of engineering, and Nazia, with a first class degree in English literature. They came to England to study from Dhaka in Bangladesh, and planned to return, but the war of independence in 1971, in which Sharif’s brother was murdered, sends them sorrowfully back. England must now become their permanent home.

The street in which the two households live is prosperous and not especially welcoming to immigrants. At a summer party, where one of the children chokes on a fruit stone, Dr Spinster leaps over the garden fence and performs a tracheotomy with a Biro, thereby saving his life. From that day, the stories of the two clans are entwined, to sometimes comic effect.

In Hensher’s perpetually spinning structure, each character is given their moment centre stage, from Leo Spinster, the son who leaves Oxford after only a term, and his brother Hugh who becomes a well-known actor despite two words ringing in his head: “five foot”. There’s neurotic, shy Lavinia, and Blossom, a dynamo of energy with repellent children, rich husband, and a kind heart. She takes in Leo’s son from a failed marriage, thus consigning the boy to years of bullying by his cousins and classmates. Much later, his childhood subjugation is revisited in S&M clubs, where he likes to be collared, leashed and whipped.

The Spinster saga rambles wildly. That of Sharif and Nazia and their brood is more focussed, perhaps because the core of it is tragic. When Sharif and Nazia, with their baby daughter Aisha, return to settle in their homeland, the eruption of the Bangladesh war of independence shatters their plans. As the Pakistani military move in, imprisoning, torturing and murdering Bengali nationalists, Sharif’s brother Rafiq is taken for questioning, never to be seen again. Rafiq’s story is lifted, Hensher tells readers in an end note, from that of Shahidullah Kaiser, one of many writers and intellectuals killed in the conflict. The officer who arrested him, and is held responsible for his death by torture, is named because, as Hensher writes, this man “may still live in protected retirement, untroubled by his deeds...I would not shield him by a change of name.” None of those who carried out genocide in the end days of the war has ever faced justice. And, Hensher seems to suggest, in their harnessing of religious zealots to help their campaign of destruction, the ground was laid for the curse of violent Muslim fundamentalism now upon us all.

It is from this bloody struggle that the novel takes its title: “The war was a month old,” he writes, “when a new name started to be heard... The Friendly Ones.” Only they were the opposite of friendly. The title of these thugs and assassins is neatly counterpointed by the family’s experience in England, where neighbours are classified as those who are, and are not, friendly. Thus two extremes of meaning tie the threads of the novel together.

The treacherous relative who betrays Rafiq is a wonderfully sinister individual, an ever-returning presence throughout a narrative that covers almost fifty years. But it is in the characters of Sharif and Nazia that Hensher has created one of the most memorable couples of recent fiction. They not only sing, but fascinate. Equally intelligent, with very different personalities, they stand at the heart of the novel, the firm lock that holds everything, confusing though it can be, in place. And confusion, though at times frustrating, is inevitable and perhaps even deliberate, mirroring as it does the teeming collision of ideas, experiences and facts contained in this invigorating work.

Courageous, humorous Sharif and Nazia take on the English on their own terms, while never forgetting their private history. On holiday in Umbria, they wake to a fusillade of gunfire, and are filled with terror before realising that it is the start of the hunting season, and they are not under attack, as they were in Dhaka. They can laugh afterwards, but with this scare, “they discovered what had stayed with them and always would.”

Their start in Britain is very different from that of many less wealthy and educated immigrants today, but in certain respects their story is universal: behind the veneer of seamless integration lies a realm of which their indigenous neighbours cannot know or imagine. Only as home-grown terrorism starts to blight the country do locals begin even faintly to understand what some incomers have suffered.

The Friendly Ones is a reminder of the pleasures found in the 19th-century novel: a passionately felt story that is expansive, questioning, baggy, highly political, occasionally self-indulgent, and utterly absorbing. Those in search of good company will find it here. Those looking for the perfect sentence or literary elegance, will not. There is barely a line that is remarkable, and several that are downright bad. But the propulsion behind the story, and the flavour and immediacy of the whole are deeply and winningly impressive.