HE HOLDS tightly onto my arm as we return from our interview in a local cafe. We are going to the London Film School for the showing of a documentary he has been lending his name to.

The passers-by, tourists and Christmas shoppers buzzing around Covent Garden may struggle to believe that the man walking beside me is a veteran of the anti-apartheid struggle and a former commander of the Umkhonto we Sizwe paramilitary forces co-founded by Nelson Mandela. He is Ronnie Kasrils — one of the best recruiters in the African National Congress (ANC).

Kasrils’s visit to London is not just another of his speaking tours. This time he is here to celebrate a story rarely told: how he recruited dozens of young men and women in Britain to join the fight of the ANC in a time when the party was fighting for its life.

Director Gordon Main is making a documentary about the London recruits. But why did the ANC need twentysomething Brits to lead risky missions in South Africa? Why did these people risk their freedom and their lives for the lives and freedom of those living a whole continent away?

Back in the cafe, sipping on a cappuccino, Kasrils had told me: “The background is the collapse of our movement in South Africa, with the blows of the Rivonia arrests [which led to Mandela’s imprisonment] and Communist Party arrests, ANC and then Bram Fischer.

“There were attempts to keep an underground apparatus going but by 1965-6 we had no structures in South Africa. There were members lying low. Most were in jail, others in exile and quite a number executed at the gallows, [sentenced to] life imprisonment, died in torture under interrogation, etc.

“So it was a reign of terror. Security police and government were boasting to the rafters that they had broken the resistance of all of the ANC and the Communist Party.”

Kasrils himself was able to escape to Odessa in the then Soviet Union, when the ANC was actively sending many of its members to do military training across the globe.

When he returned from training, leading ANC member Oliver Tambo ordered him to come to London and help him with a master plan. It was a simple stroke of genius, Kasrils admits: the idea of recruiting white Londoners who would come to South Africa in disguise on a series of missions.

They would pretend to be tourists, honeymooning couples, businessmen or students and — without the suspicion black people would face from the South African Police — set off leaflet bombs and deliver incendiary speeches to the black population. Then they would swiftly return to London, back to their ordinary lives.

“But why London?” I asked, imagining the city I live in filled with revolutionary hearts crossing the street anonymously today without the faintest fanfare over the service they gave to win the freedom of a nation.

He replied: “Because in London, although so much further from where we had our bases (Zambia and Tanzania), the links with South Africa are multitudinous. There’s business and communications and shipping and flights.”

And who were these men and women? How did the then 27-year-old Kasrils, fresh out of Soviet training after years working as a scriptwriter and film director, connect with these radical youths?

“I came here, I registered at the London School of Economics (LSE) and then — with the Young Communist League through their organisers, and through my own connections — began to recruit people who wouldn’t know that others were involved as well,” said Kasrils, adding that most were young working-class people, usually in trade unions.

“At the same time I also recruited students from the LSE, people like you,” he pointed at me — I’d already told him that I come from a colonial family myself and have a masters degree in politics from another University of London institution.

“People who were middle class but fired with the anti-apartheid cause, which in the 1960s and 1970s and onwards, was magnetic,” he continued. “Although we call it London recruits, that’s because here is where we recruited largely, but we recruited elsewhere. We drew in not just Londoners. There were people who were American or Greek, Irish, Scots, Welsh and so on.”

He took a sip of coffee, waved in the air with his left hand and wiped the sweat off his face. “I’d been with them on demonstrations, been with them in the university pretending to be a scholar, in scrapes, in detention at demonstrations … With the Young Communists, from the Communist Party, who also linked with the dock workers here and in Liverpool. They knew their members so I would discuss the type of profile, the type of people we were looking for.”

Then he would walk with them in Hyde Park, sometimes hold more than one encounter until he knew that the profile was the right one. After that they were off, packed with fake-bottomed suitcases filled with leaflets and mild explosives. Few directions were given other than they had to look for the hotspots of the black population’s daily lives: train stations at rush hour, markets, high street corners.

I got the chance to see them in person, these men and women, now in their sixties and seventies. In the theatre of the London Film School they all huddle together in groups, a collegial mood buzzing through the room.

Two middle-aged women next to me giggle and I find out they both set off leaflet bombs in the streets of Johannesburg and Cape Town. To them their actions were an inevitable result of believing in the cause. Nothing else mattered.

Nothing else matters in this moment either, other than the joy of reminiscing about one’s youth. Yet for everyone else in that room, these men and women did something a lot larger than a mere youthful act of selflessness. As Kasrils put it, they gave the ANC “breathing space” to regroup and re-establish itself. They gave a monumental struggle the chance to resurrect itself and deliver a fairer, more democratic South Africa.

• If you’d like the see London Recruits come to your local cinema even sooner, you can crowd-fund it by going to London Recruits Kickstarter Page