"It's an honour to be working with Ken on a project like this," says the footballer-turned-actor Vinnie Jones. He's not alone in feeling that way: among the cast of Ken Loach's new film, Looking for Eric, there is a palpable sense of excitement. With an estimated budget of $150m, the first cinematic re-creation of Britain's tragedy in Vietnam is bound to be a box-office hit. Yet already the vultures are circling. "We don't want Ken Loach," says the Vietnam veterans' spokesman Paddy Ashdown, "and we certainly don't want this film."

Adapted from Alistair MacLean's Booker-shortlisted novel, Looking for Eric is the story of five Royal Marines who go in search of a missing comrade in the Mekong Delta. Back in 1973, the book was a huge hit, crystallising public opposition to our commitment in Vietnam. By this stage, British troops had been there for six years, sent by Harold Wilson in return for America's help with propping up the pound. At the time, Wilson promised they would be there for just six months. How wrong he was.

Wilson's decision to send in the marines cast a long shadow over British life in the 1960s and 1970s. When the Labour Party split and he fell from office in 1969, many thought the boys would be coming home, but Ted Heath defied expectations and kept them in - another deal, some said, to win American backing for the war in Rhodesia.

Casualties mounted; in London, demonstrators camped for night after night in Parliament Square. But despite all the protests, despite the

anti-war records by the Beatles, Slade and even the Wombles, Britain stayed in until the bitter end.

As Britain lost more than 2,500 men in Vietnam, it is hardly surprising that the scars remain painfully raw. At Norman Foster's unconventional memorial on Pall Mall, it is not unusual to see families with tears in their eyes, while defenders of the war continue to pump out hugely popular books. Christopher Hitchens's A Noble Cause, for example, was Britain's bestselling title last Christmas, while this year brings the reissue of Max Hastings's justly celebrated battlefield reports for the Evening Standard, which did so much to bring home the suffering of the ordinary squaddie.

That it has taken until now for Loach's film to get funding is a reminder that the old passions have yet to fade. Melanie Phillips's Facebook petition, urging people to boycott Looking for Eric, has already picked up 120,000 signatures. But not all veterans oppose it. "I'm looking forward to it," says the Labour leader, David Davis, who fought with the SAS in the desperate last defence of Saigon, "because I think anything that reminds us of the horrors of war can only be a good thing."