On a December evening in 1938, a large crowd gathered at London's Victoria station. They were joined by the future Labour prime minister, Clement Attlee, as they waited to welcome home 305 British volunteers from the Spanish Civil War. More than 500 of their comrades had been killed, fighting for the democratically elected government. Its defeat left the country in the hands of General Franco, a brutal dictator who stayed in power for decades.
The British Battalion of the International Brigades has been celebrated in books and poetry but the exodus of 2,500 men and women to fight in a foreign civil war alarmed the British government. Recently released files show MI5 kept a close eye on the volunteers. Ministers even considered using the 1870 Foreign Enlistment Act to stop the flow, but no one was prosecuted.
The parallel with modern-day Syria is not exact, especially now that groups linked to al-Qa'ida are taking a prominent role in the battle against Bashar al-Assad. But I can understand why idealistic young people are once again being drawn into a foreign conflict. A handful of British citizens has already been killed in Syria, including Brighton student Abdullah Deghayes, 18, who died fighting in Homs. Abdul Waheed Majeed, 41, from West Sussex, appears to have become the conflict's first British suicide bomber; he blew himself up outside Aleppo prison in February.
It is easy to see why our government is alarmed by Majeed's "martyrdom". But I'm uneasy about the Home Office's underlying assumption, which seems to be that anyone who wants to fight against Assad is a threat to the UK.
Last year, the Home Secretary, Theresa May, used her powers to strip British passports from 20 individuals who had dual Syrian-British nationality. Presumably she had reason to believe they posed a danger, but now the authorities' rhetoric has changed.
In a new campaign spearheaded by the police, Muslim women are being asked to take a bigger role in preventing young men from going to Syria to fight. Inevitably, this has been denounced in some quarters as tantamount to spying for the government, but the initiative has the support of some prominent Muslims. The brilliant Sara Khan, director and co-founder of the Muslim women's organisation, Inspire, points out that work to explain the sectarian nature of the war, and to counter the influence of extremist videos, has been going on behind the scenes for ages.
Every generation throws up a conflict which horrifies decent people. The rest of Europe left Franco to murder his way to power, supported by Hitler and Mussolini. Assad is just as ruthless, and he's supported by Russia, China and Iran. Of course I don't want to see more British teenagers dying in Syria. But we need to think about how to keep them safe, instead of treating them all as potential terrorists.