It is not often a critic wishes a play were longer. In the case of this ambitious account byHoward Brenton of the partition of India in 1947, however, I found myself craving more than two-and-a-quarter hours. Brenton crams an amazing amount in but still leaves me wishing he had explored alternative scenarios to the hectic timetable for Indian independence.

Brenton’s focus is on Cyril Radcliffe, the British judge deputed by Clement Attlee to work out the division of the Indian subcontinent on Hindu and Muslim lines in the space of five weeks in 1947. Ignorant of India, mathematics or map-reading, the principled Radcliffe finds himself the victim of despair, as well as Delhi belly, and enmeshed in a whole series of escalating conflicts. One is between Nehru’s Congress party and Jinnah’s Muslim League. But Radcliffe is also caught up in an ideological battle between his two secretaries, as well as a marital one between the Viceroy, Lord Mountbatten, and his adulterous wife, Edwina.

Even if Brenton’s play raises more questions than it can answer, it gives a vivid picture of the pressures of the time. While Nehru and Jinnah are driven by high ideals as well as practical politics, Radcliffe wrestles with whether to locate Calcutta in India or the newly created Pakistan, and Mountbatten cynically talks of a hundred thousand deaths as “an acceptable level of violence”. Brenton knows how to make history manifest. He is also excellently served by Howard Davies’s production, which whisks us through the play’s 25 scenes with cool clarity, and by the 17-strong cast. Tom Beard is all rattled decency as the harassed Radcliffe, Silas Carson and Paul Bazely lend Nehru and Jinnah an iconic stature, and Andrew Havill and Lucy Black as the Mountbattens show how a private breakdown has public consequences. Brenton’s play may not be the last word on partition but, as when Jinnah claims that the British always favour Hindus whereas they see Islam as “iron-grey and frightening”, it has considerable topical resonance.

The Partition of India is a massive subject but in this powerful new piece Howard Brenton has had the fertile idea of approaching it from the perspective of a forgotten but crucial player.

Cyril Radcliffe was a British judge who knew nothing about India or maps but, in 1947, he was sent there by Prime Minister Clement Attlee to draw the line that would divide the sub-continent into two separate states. To add to the black absurdity, he was given just five weeks to complete the job.

Premiered in Howard Davies’s lucid, elegant production, the play presents Radcliffe (excellent Tom Beard) as a tragicomic figure – a decent man who is driven to despair by the gradual realisation that, whatever he does, there will be a bloodbath.

A cynical hypocrite in Brenton’s estimation, Viceroy Mountbatten (Andrew Havill) declares that 100, 000 deaths would be “an acceptable level of violence” and the play speculates about the pressures he may have brought to bear on Radcliffe because of his wife Edwina’s affair with Nehru (a magnetic Silas Carson). It’s a fascinating play which views colonial culpability from an unexpected and singularly revealing angle.

It’s a promising idea to examine the subject of the independence of India and the creation of Pakistan via the drawing of a line on a map.

Howard Brenton’s tactic, in his third play for Hampstead in 14 months, results in a slick work that leaves us, unusual for historical drama, wanting a little more.

The poor sap saddled with the task of dividing the subcontinent in 1947 without inflaming the passions of Hindus and Muslims alike was judge Cyril Radcliffe (Tom Beard), who knew nothing about India or maps and had a mere five weeks to complete the work. Plunged into a maelstrom of vested interests, he becomes increasingly desperate as he contends with canny politicians Nehru (Silas Carson), Jinnah (Paul Bazely) and Gandhi (Tanveer Ghani). The Mountbattens float tantalisingly on the sidelines, as does Prime Minister Clement Attlee, anxious to be rid of the financial burden of empire.

Tim Hatley’s minimalistically opulent set of filigree screens suggests a place of hot days and heated tempers, as Beard presents a good man going to pieces under great strain. No one could accuse Hampstead of under-resourcing this play; director Howard Davieshas a cast of 17, although not all of them have much to do. An arresting final image reminds us of the ongoing consequences of Radcliffe’s endeavours.

At first sight, Cyril Radcliffe appears an unpromising protagonist. When we first meet him in Howard Brenton’s new play, he seems decent but dry: a nice, intelligent, principled man. But on his decisions, millions of lives will depend. Radcliffe was the man sent by Clement Attlee to India in 1947 to draw the line that would mark the border between India and Pakistan. He had no experience of cartography, had never been to the Indian subcontinent and had only five weeks to complete the job. Brenton, facing an epic task himself in distilling the turmoil of partition into two hours on stage, seizes on these astonishing facts and spies a way in. It is through Radcliffe’s eyes that we encounter the tumult, violence and conflicting demands; it is through his gradual disintegration into dishevelled, despairing disillusionment (excellently portrayed by Tom Beard) that we sense the impossibility of the task, and it is through his regrets that the play makes its points about legacy.

Brenton is a masterly storyteller and the play expertly draws you into the maelstrom.Howard Davies’s skilful production, focused on the interiors (suggested by designer Tim Hatley through elegant filigree screens) in which the decisions will be made, makes you constantly aware of the turbulence outside.

Meetings descend into shouting matches as Radcliffe keeps drawing and erasing the line, becoming ill and frantic as he realises that whatever he does, thousands of people will die. The absurdity of his situation is more eloquent than any strident comments would be, and so Brenton, by keeping his focus tightly on one British man, makes you acutely aware of the impact on millions of individuals.

Playwright Howard Brenton has done one of his historical re-creations on the last days of British rule in India. He focuses on Sir Cyril Radcliffe, a mouselike London lawyer who was despatched to Delhi to draw (in five weeks) the border separating India from Pakistan.

Mr Brenton chooses his subject well. Radcliffe is an obscure figure and therefore one about whom we are unlikely to have a prior opinion.

In 1947, he seemed to bring similar innocence to the sub- continent. His very lack of familiarity with India was the reason he was chosen for the task by Clement Attlee (a deft cameo by John Mackay).

Even before Radcliffe gets to Delhi he is the subject of speculation. Someone says: ‘He’s not a fool.’

Director Howard Davies depicts all this in the pressure cooker of a pavilion in the Viceroy’s garden, where Radcliffe (Tom Beard) holes up.

Mr Beard gives him a sympathetic portrayal, anguished by the partition task. And what a fiendish task it was. India was ‘a subcontinent of nationalities with 2,000 ethnic groups’. In the Punjab, which had to be bisected by the border, there was no easy geographical allocation according to religions.

Imagine the scene: out of the blue the prime minister asks you a favour. Would you decide how India should be partitioned for him? You know nothing about the subcontinent or its politics, and there’s absolutely no chance of satisfying the demands of the groups involved in this huge geographical carve-up but you say yes anyway.

It sounds fantastical but that’s what happened in 1947 when Clement Atlee summoned Cyril Radcliffe, a judge who cited a trip to Venice as his biggest adventure abroad, and told him he had five weeks to settle the boundary between India and Pakistan.

Howard Brenton’s tale of Radcliffe’s delirium-inducing visit to the British Raj sees him confidentally sketching a series of portraits of major 20th-century political figures (Nehru, Gandhi, Jinnah, Atlee et al).

It’s a big story, with a lot of background information and cartographical detail to be conveyed. But it’s economically and resonantly told in Howard Davies’s smartly designed, well-acted production.

Vivid phrases tumble from characters’ lips as they try to decide whether Radcliffe is an assassin sent to murder India, a comic actor in a Gilbert and Sullivan opera or (in the flailing Radcliffe’s own assessment) the patsy of the gangsterish imperial powers-that-be. It’s well worth a visit to Hampstead to make up your own mind.

Partition is a dangerous game, and the consequences of “drawing a line” in 1947 to create a Muslim homeland in Pakistan, leaving the rest of India as a secular home for the Hindu majority, was particularly disastrous.

It’s the background to this almost farcical process of colonial disengagement by the British and arbitrary segregation by a civil servant, Cyril Radcliffe, who knew nothing about India and nothing about maps, that is the subject of Howard Brenton’s fleet and fascinating new historical drama.

The origins of the piece as a project for the screen sometimes show through, but many plays come about this way, and Howard Davies’s lucid production succeeds in marshalling a large cast of characters – including the Mountbattens, Nehru (first Indian ruler after the British), Nehru’s mentor, Gandhi, and the leader of the Muslim league, Muhammad Ali Jinnah – with skilful purpose.

The British prime minister, Clement Attlee (a too tall but suitably finicky, pipe-smokingJohn MacKay), sets a timetable of just five weeks for Radcliffe (Tom Beard, strikingly similar to Colin Firth) “to lift the yoke of imperialism,” while all factions bicker at the Viceroy’s front door, Gandhi (a fragile Tanveer Ghani) remains aloof to politics, and Lucy Black’s vivacious Edwina Mountbatten tries to manoeuvre her torrid affair with the charismatic Nehru of Silas Carson into a bartering block of influence.

And at the centre, Brenton creates a tragi-comic figure in Radcliffe, dealing with the problem in cricketing terms (he wants, impossibly, a “level playing field”), assailed by dysentery, driven to despair by his own increasing realisation of compromise and failure, and finally visited by the Lord Krishna in a dream before he picks up his fateful pencil.Andrew Havill’s imperious, bony-featured Mountbatten is no help at all, keen to get shot of the lot of them.

Whatever fictional twists to character and incident Brenton provides, there’s no doubting either the momentousness of what happens, shadowed by past riots and outrages, some of which atmosphere spills into the mosque-like cane and wicker design of Tim Hatley; or the sense that an entire continent is poised on the brink of calamitous upheaval and unrest.

How far did the affair between Lady Mountbatten and Nehru affect the drawing of the boundary between India and Pakistan in 1947? It’s one of the rum questions that Howard Brenton raises in his lively political drama. Encouraged by Mountbatten, the Labour government allowed just five weeks for the boundary to be decided by a judge who had never been to India before, and knew nothing of the political scene. Cyril Radcliffe (a harassed Tom Beard) is nobly determined to give it his best shot, despite a bad attack of Delhi belly. Brenton concentrates on the jostling characters who surround Radcliffe, including Silas Carson’s politically astute Nehru and Paul Bazely’s intellectual Jinnah. The play could easily be a dull history lesson, but once again Brenton illuminates the pressures and strains behind a crucial moment in history.