Fifty years ago Britain had just emerged from the coldest winter of the 20th century when some protesters emerged to stoke the fire of protest and rattle the establishment. The Spies for Peace, as they called themselves, were a small group of peace activists who not only marched and shouted, but also broke into a government bunker, stole the secrets they found there and published the then Conservative government's plans for the aftermath of nuclear war.

The Spies for Peace were young and idealistic, but they were also smart. They wanted to break the secretive absurdities of the state, but they did not want to be arrested for doing so. Only my late father, Nicolas Walter, has previously been named as one of the group, and now, 50 years on, my mother, Ruth Walter, is also happy to be identified.

The Spies secretly created a pamphlet in which they explained what they had discovered about the regional seats of government that would spring into action in the event of nuclear war. They duplicated 3,000 copies of the pamphlet, destroyed the originals, even threw the typewriter they had used into a canal, and posted them to members of the peace movement, plus journalists, celebrities and MPs.

"We thought the press might ignore it, that they would be in cahoots with the government," my mother told me, remembering the day when the secret was finally, unstoppably, out. That day also happened to be in the middle of the Easter Aldermaston march, and her 21st birthday. "The headlines, the splashes, the fury – we hadn't counted on that. We sang We Shall Overcome in the sunshine that day – and yes, I think we believed that we would."

With all the reminiscing that we have been doing lately, it is very hard to be sanguine about where that optimism of the 1960s has ended up. When I ask my mother if protesters could do something similar today, her initial reaction is negative. "How could you, with all the cameras around? We only had to worry about fingerprints and phone taps. We may not have realised it at the time, but we could do things without surveillance that would be so hard today."

Even so, those optimistic days of protest and song were not all for nothing. The Spies for Peace did not, as they hoped, usher in an age of nuclear disarmament and government openness. But their influence did not begin and end in April 1963.

No government now, after all, would hatch a baroque and secretive system for surviving nuclear war; the very idea would be seen as the delusory folly it was. And the Spies were part of the much wider movement of liberalisation which has come to characterise the 1960s, the time that transformed a grey and deferential Britain into something much more colourful and questioning. Another of the spies, who still chooses to be anonymous, said to me years ago: "The idea that people had to spy on their own government to get the truth out, this was a very fertile idea, the idea that it was right to ask questions, to battle them for the truth."

And the history of civil disobedience, on which the Spies for Peace were building, never disappeared. This week, many people have remembered the Thatcher years not by discussing her legacy but, instead, the fertile legacy of the protests that arose against her, from the miners to Embrace the Base, Stop the City to the poll tax protests. This government's adherence to the harshest forms of capitalism has been, and will be, challenged in the streets by those who continue to believe in an alternative.

This is not to say that all the left has to offer is a condition of permanent protest. It is surprising how often protest can be successful, as ideas which were once seen as a radical filter into the mainstream. Every step for liberty and equality that has been taken in this country started at the grassroots. As Nicolas Walter once wrote in a book called About Anarchism: "No one can tell when protest might become effective, and the present might suddenly turn into the future."