It was a generous Christmas present, and most of us would have been grateful.

Yet, after their release three months early under President Putin's well- publicised Amnesty Bill, the members of Pussy Riot who were serving two-year sentences expressed nothing but scorn at their good fortune. The amnesty, they said, was a mere gesture, intended to make Russia look good ahead of the winter ­Olympics in February. Nadezhda ­Tolokonnikova who, like fellow singer-protestor Maria Alekhina, served her time in a penal colony in Siberia, said she feared for ­protestors whose trials would take place after the Olympics, when Putin was likely to demand more severe punishment.

Some would argue the Pussy Rioters were themselves severely punished. Few can forget the footage of their cacophonous impromptu concert, staged in a Moscow cathedral, in which it looked as if a bag of electrified jelly babies had been let loose. In dresses and balaclavas, the anarchist group sang "Mother of God - Chase Putin Away!", calling on the Virgin Mary to get rid of the Russian leader, and to become a feminist like them. To my mind their only sacrilege was to massacre Rachmaninov's Ave Maria, but even among their defenders many were outraged they had desecrated the church in this manner.

But, like all born rebels, criticism does not puncture them. Speaking after their release last week, Alekhina and Tolokonnikova were models of defiance. With nails painted a war-like red, Tolokonnikova said she and her fellow Pussy Rioters still want Putin removed from power. Now, however, they also have a new aim: to bring about radical penal reform.

Their fighting spirit is admirable. It's almost as if the suffragettes of old have been reborn: unrepentant, fierce, and uncowed. Only a few hours earlier they had been incarcerated in Mordovia. As prisoners there like to say, "Those who never did time in Mordovia never did time at all." The conditions in which inmates live and work reads like something from one of Solzhenitsyn's darker chapters. Conditions were so bad that at one point Tolokonnikova went on hunger strike.

Yet it was Alekhina's allegations that attracted most attention on their release. Before and after visits from her lawyer, she says she was subjected to gynaecological examinations. Both women report regular sexual assaults and violence towards inmates, along with a catalogue of other miseries, including alleged murder.

Now freed, they intend to improve the system from beyond the walls. One hopes this pair are not to be played with, in the old cat-and-mouse tactics used to break suffragettes, where they were let loose for a period to recover their health and then recaptured. Judging from their mood after their ordeal, however, they are made of tungsten. If anyone can survive, they can.

In this too they remind me of the suffragettes, whose courage in the face of police callousness, prison brutality and public opprobrium was extraordinary. The group cannot be unaware of the historic parallels, since one of them - known only as Serafina - says her main influences include Emmeline Pankhurst.

From hunger strikes to acts of public disorder and hooliganism, they share the suffragists' diehard moral outrage and physical bravery. Willing - almost eager - to break the law, they remain steadfast in their political principles. Admittedly, the Pussy Riot agenda is far wider than that of Pankhurst and her followers, who had a single goal and stuck to it. Not so with the anarchist group. Anti-capitalist but also against all authoritarianism and discrimination, their feminist battle cry is in danger of being drowned out by their litany of grievances. As their name suggests, however, women's rights remain at the heart of what they do. Now to that purpose the label reformer must be added.

To change the penal system would be truly revolutionary. When Elizabeth Fry campaigned to improve Victorian gaols, she was working against the forces of ignorance. Putin's Russia is far more frightening. Yet no doubt the Pussy Rioters are already sharpening their wits, anticipating the challenge ahead. Again, they are precisely like those suffragettes who risked their lives - and sometimes lost them - in the name of a great and just cause.