In The Observer, Rachel Cooke writes:

In 1999, shortly after his film about the British peace-keeping force in Bosnia, Warriors, was screened by the BBC, Peter Kosminsky received a letter. It was from an old soldier, who had found Warriors moving, and wanted to thank its director. At the end of the letter, though, was a line – thrown out more in hope than expectation – that caught Kosminsky’s eye. “You should do a film about the British soldiers who were in Palestine,” it said. “No one remembers us.”

As psychological bullets go, this one was well aimed. Kosminsky is nothing if not in the business of remembering. The kind of things that governments like to forget are his stock in trade. Down the years, he has made films on a variety of uncomfortable subjects, from the activities of the police in Northern Ireland (Shoot to Kill) and New Labour control-freakery (The Project), to British-born Muslim suicide bombers (Britz) and the suicide of Dr David Kelly (The Government Inspector), each one trailing controversy – if not always a sudden bout of recovered memory on the part of the establishment – in its wake. The soldier’s letter was duly passed to Kosminsky’s researchers, who began interviewing veterans.

Between 1945 and 1948, some 100,000 soldiers served in the British-controlled Mandate of Palestine. Kosminsky’s team spoke to around 80; he found the men’s stories to be both gripping and moving, so he carried on, wading next through letters, diaries, memoirs and history books. Slowly, a theme began to emerge. “The thing that came out most strongly,” he says, “was that the men all arrived in Palestine feeling incredibly pro-Jewish. A few of them had helped to liberate the [concentration] camps, so they had seen what had happened [to the Jews] with their own eyes. And everyone had heard the stories and seen the newsreels.

“When Jewish refugees arrived in Palestine off the boats, and were caged and beaten by British forces [the British placed strict limitations on Jewish immigration to Palestine], many soldiers didn’t like it all. They knew what these people had been through. Over time, though, the soldiers’ attitudes changed. Some of this was just the usual British support for the underdog; there’s no question that by 1948 [when Israel declared itself an independent state] the Arabs were perceived as that. But also, if you’re being attacked on a daily basis [by the Jewish resistance], if you’re under constant threat of kidnap, if you’re confined to barracks behind a lot of razor wire, your feelings are bound to change.”

Kosminsky’s first idea was to make a drama about a British soldier who would exemplify this shift. “I suppose it started out as standard Kosminsky fare, which was pointing the finger at Britain. First of all, these men don’t have a memorial; they’re forgotten. It’s only recently that they were allowed to march to the Cenotaph. When they came back to Britain, no one wanted to know; pulling out of Palestine was a terrible humiliation, a total defeat. Second, we were the colonial power in Palestine and, as in so many other examples of our retreat from Empire, we left it totally fucked up. Chaos. We washed our hands of it. I wanted to say: if you think the Israeli-Palestinian situation is not our problem, think again. We were there, we left, and 60 years later, it is still a problem.”

The trouble was, something else kept nagging away at him. “The more I read their stories, the more I began to be struck by some odd parallels,” he says. “For instance, if there’s a suicide bombing in Israel, usually the Israeli Defence Force immediately goes [to the West Bank or Gaza] and blows up the house of the bomber. I’d always assumed this tactic had been invented in the modern era. But in the veterans’ interviews, they described doing exactly the same thing. When a member of Etzel [the Israeli name for Irgun, the Zionist paramilitary group that operated in the Mandate of Palestine from 1931 until 1948] or Lehi [better known as the Stern Gang, another militant Zionist group] attacked them, the British would find the family home and dynamite it.”

On the other side stood the Irgun, as ruthless as any 21st-century terrorist organisation. When the King David Hotel in Jerusalem, which served as the British Mandatory authorities’ headquarters, was bombed in July 1946, 91 people died, many of them civilians. “They were extremely effective. You only have to compare the attack on the King David to something like the Brighton Bomb [in which the IRA killed five people] to see that. There’s a moving memoir by the colonial secretary, who survived. He spent a week attending the funerals of his friends, became unhinged and had to be invalided out. He lost his reason.”

Somewhere along the line, Kosminsky decided that his film would need to tell two stories: one set in the Mandate of Palestine, the other in Israel, 2011.

Eleven years later and the result of all this research and ambition is shortly to be screened on Channel 4. Was it worth it? I think it would have been worth it if it had taken him twice as long. The Promise, which will be screened in four parts, and runs to some seven and a half hours, is the best thing you are likely to see on television this year, if not this decade. It is not only that it is so exciting, moving, and full of exquisite performances; it’s also that the extraordinary detail and thoughtfulness of it – the sheer scale of the canvas on which its director works – subtly imparts so many emotional and factual truths that you feel your own allegiances, whatever they may be, suddenly shifting uneasily, sometimes on a minute-by-minute basis. Revelatory is an overused word, but The Promise is exactly that: the power of its storytelling will open eyes more effectively than any leaked document, any piece of rhetoric, any news bulletin.