Thirteen years after the end of the Second World War, Belgium played host to the first world's fair since hostilities ceased.

Built on an enormous site in Brussels, Expo 58 was three years in the making and was open to the public for six months. Members of countries from all over the world, from Mexico to Austria, the USA to the USSR, congregated at this commercial and cultural extravaganza, whose mood reflected a possibly naive but heartfelt wish that the future would be rosier than the recent past.

Jonathan Coe pitches his hero, Thomas Foley, into this diplomatic playpark. A junior civil servant in the Central Office of Information in London, he has been chosen to superintend Britain's piece de resistance at the fair, a replica English pub called The Britannia. Foley cannot understand why he has been selected for this dubious honour but his bosses think him perfectly suited: his father once ran a pub and his mother was Belgian, even though she escaped the country as a child with her mother, only hours before the rest of her family were killed by the advancing German army.

Thomas, who is married with an infant daughter, is at first aghast at the prospect of being so long away from home. Swiftly, however, he comes to see this as a blessed respite. Coe sets the dreariness of Thomas's home life against the exciting prospect of Expo 58. Home is Tooting, baby's gripe water and Sylvia, a wife with whom increasingly Thomas realises he has little in common. Worst, perhaps, is the mood that pervades this leafy backwater: "he had begun to feel himself driven almost to distraction by the smug quietude of that deathly suburb, the overwhelming sense of indifference towards the great events that were taking place out in the wider word."

Expo 58, on the other hand, looks to the future: "Here, for the next six months, would be thrown together all the nations whose complex relationships, whose conflicts and alliances, whose fraught, tangled histories had shaped and would continue to shape the destiny of mankind."

Starting prosaically with a resume of the key facts about the world's fair, the novel continues in the same low-key vein, though with thankfully fewer facts and figures. Depicting office and home life in shabby, dull London, Coe offers his first glimmer of humour in his scenes of civil service behaviour, and the appearance at a top-level meeting of a mysterious duo who behave, as the novel progresses, like an espionage version of Morecambe and Wise.

When a bureaucrat declaims, with a broad wink to the reader, "One thing's certain - those pavilions are going to be crawling with spies..." it's clear how the plot will unfold. If one expects high comedy, though, disappointment awaits. Coe's handling of events is decidedly flat, thus matching the personality of Thomas, who never really comes to life. Only when the counter-espionage double-act get into their stride, with their spritely, camp dialogue, is the reader likely to smile.

Elsewhere, however, Coe's tone is far from droll. At the Edinburgh International Book Festival Coe remarked that this novel is a mix between "John le Carre and Evelyn Waugh", with a touch of Ealing comedy thrown into the brew. That might have been his aim, but for this reader its predominant mood is of melancholy, bitterness and regret.

There's nothing wrong with that, of course. In fact, in light of its central theme, of espionage and lies, of dangerous political and personal deceptions, of the kind that forever ruin lives, that is entirely appropriate. As Foley, alone abroad, falls first for one girl and then another without mentioning he is married, his wife at home appears to be flirting outrageously with a neighbour.

His faltering marriage plays a far more significant part in the plot than the skulduggery he begins to suspect his new foreign acquaintances of conducting. The seriousness of this domestic strand, and the simple, affecting way in which Coe handles it, makes the slapstick humour of the underpinning espionage grate. That mismatch might nevertheless have knitted into a coherent whole had it not been for Coe's heavy hand with period detail.

So thorough in his descriptions of the Expo that readers could reconstruct it inch by inch for themselves, he writes as if a ton of factual cement is glued to his boots. Among his many acknowledgements are thanks to those in Belgium who have helped in the writing. This may explain the devotion to historical accuracy, but sadly it does nothing to lift the novel out of its doldrums or put some much needed spirit into its sails.