It was a momentous year. In 1963, we had the Profumo scandal and the first Beatles LP, the National Theatre company was created under Laurence Olivier and the Royal Shakespeare Company became a global force with Peter Hall's production of The Wars of the Roses. But over at the other Stratford, in the east end of London, a show opened with an equally devastating impact. It was Oh What a Lovely War and its originality lay in the fact that it viewed the first world war from the perspective of the common soldier, and that it counterpointed songs from the period with grim battle statistics that appeared in a running newsreel tape above the stage.

I remember rushing down from Lincoln, where I was working, to see it and being bowled over by the genius of Joan Littlewood's Theatre Workshop production: its ability to captivate with its fluidity and grace, and to arouse one's anger at the attritional strategy of the military top brass. To suggest, as Michael Gove did recently, that there was something unpatriotic about Oh What a Lovely War because it adopted a critical stance is to offer an insultingly narrow definition of love of country.

Why did the show, now being revived to acclaim in its original home by the director Terry Johnson, make such a long-lasting impression? I found one clue in a review of Littlewood's original production in the theatrical magazine Encore. "This is the end-product not of four or five weeks' rehearsal," wrote Charles Marowitz, "but of 10 or 12 years of tension and discovery at Stratford East."

Theatre Royal at the time of the original production of Oh What a Lovely War (1963). Photograph: Romano Cagnoni/Theatre Royal Stratford East Archive Collection

You could go back even further and say that Theatre Workshop's trademark style – mixing speech with song and making expressive use of light and sound – dated back to its 1945 beginnings as a travelling troupe. By the time it took over Stratford's Theatre Royal in 1953, its collaborative approach had yielded a string of startling productions that captivated critics and won foreign prizes, while attracting derisory funding from our own Arts Council.

If any living person can explain the work's impact, it is Murray Melvin. He was in the original 1958 cast of both A Taste of Honey and The Hostage at Stratford East, and was a key player in Oh What a Lovely War. For the last 22 years, he has been the devoted archivist of Theatre Workshop, presiding over an immaculately maintained library at the Theatre Royal with the poker-backed elan of a trained dancer. But, aBut, although he communes daily with the memory of Littlewood and her partner Gerry Raffles, he lives totally in the present.

The idea for Lovely War was sparked by a BBC radio programme of first world war songs put together by presenter Charles Chilton, who lost his father to the conflict at the age of six. Raffles happened to hear it. Littlewood saw its theatrical potential, devised a rough scenario, and a script was commissioned. So what happened in rehearsal? "On the first day," says Melvin, "we read the script and Joan said, 'Well, that's a load of rubbish', and we never looked at it again. All we kept was the actual title and the songs. But Joan gave the actors a reading list and got us to carry out our own research. Our bible was a book by Barbara Tuchman, August 1914, but we also read countless histories – Haig's Diaries, memoirs by people like Siegfried Sassoon and Robert Graves.

"I was given Alan Clark's The Donkeys to read and was very struck by a section on mustard gas. What hit me was a story about a division marching towards the front in an eerily silent landscape, with no birds singing. In the distance, they saw a troop of British soldiers coming towards them, staggering and swaying about as if drunk. As they got nearer, they realised the soldiers had been blinded by mustard gas. Joan had us try to recreate this by marching round and round the stage for three days. You must remember her shows were as carefully structured as a Mozart symphony. Just when we thought we'd got it right, she said, 'We'll have to cut this.' When we asked why, she said, 'It's too horrific.'"

Actor and director Joan Littlewood practising a role at a mine in Swinton, Lancashire. Photograph: Topham Picturepoint

It's a revealing story. It shows how Littlewood was anxious to confine the physical horror of the war to the savage statistics unspooling above the stage: something, Melvin reminds me, the actors never saw and scarely knew the content of until after the first night. His anecdote is also a reminder of the paradoxical nature of the show. The actors were crucial collaborators, in that they uncovered much of the basic material and had to vouch for its authenticity. If Sir Douglas Haig at one point prayed, "I ask thee Lord for victory before the Americans arrive", it is because those were his actual words.

Nevertheless, Littlewood was the ultimate boss. Above all, Melvin's story confirms she was a director whose aesthetic sense was as strongly developed as her political instinct. "One has to remember," he says, "that she was steeped in the European theatre tradition and knew all about the expressionist techniques of Meyerhold in Russia, Piscator's use of newsreel in Germany and the Theatre National Populaire's use of a bare stage and pinpoint lighting in France."

I'd say the source of Littlewood's genius, and one of the reasons for Oh What a Lovely War's instant success, was her ability to combine a European aestheticism with a deeply English love of popular theatre. The use of pierrot costumes was an inspired choice, as it anchored the show in a seaside tradition. And the presence of music-hall is evident in the way the MC (Victor Spinetti in the original production) chats to the audience as they come in, and reappears later in a hilariously unintelligible drill scene.

So what effect did Oh What a Lovely War have? It helped change attitudes to the first world war. Although we may have read the poetry of Sassoon and Wilfred Owen, we had never before seen popular entertainment express the disenchantment felt at the time by the average soldier. Looking back at the 1963 programme, it is also clear that the production was intended as a political provocation. One note reads: "In 1960, an American Military Research Team fed all the facts of World War One into the computers they use to plan World War Three. They reached the conclusion that the 1914-18 war was impossible and couldn't have happened. There could not have been so many blunders nor so many casualties. Will there be a computer left to analyse World War Three?"

On a purely theatrical level, the show also did a lot to loosen up the formal rigidity of the British theatre. It was active in demolishing the gap between stage and auditorium, promoted the growth of the musical documentary and encouraged actors to take responsibility for research and development: something that bore fruit in the work of companies like Joint Stock. And the pervasive Littlewood irony – the contrast between beguiling form and radical content – was evident in one recently revived musical: Kander and Ebb's The Scottsboro Boys, which explored Alabama racism through the structure of a minstrel show.

Melvin is excited about the revival but what really thrills him is that the Theatre Royal has invited schools around the country to devise projects exploring what war means to them now. The results, he says, have been staggering: the best eight will be staged as curtain-raisers during the run of the current show. "Joan would be thrilled," he says. "She was a pioneer of theatre in education and loved handing over the Stratford stage to the young 'nutters', as she called them. If she were still around, I don't think she'd be celebrating the Theatre Workshop tradition. Her big question would be, 'What have you done with it?'"

• 'Restores a classic for a generation': Michael Billington's four-star review

• Kenneth Tynan on Joan Littlewood's 'one-woman show'

• In pictures: Oh What a Lovely War

• Susannah Clapp on Oh What a Lovely War