Is this the defining moment for Putin's 100,000-strong army of angel-faced devotees? The mass Putin youth movement has been struggling to find a purpose, but in the wake of protests against suspected vote rigging in last week's parliamentary elections its time may have come.

Russian state TV totted up the votes in the Rostov region to a total of more than 146%. Even with Russia's patchy electoral history that's an impressive tally. This week thousands of protesters hit the streets of Moscow to vent their anger about the apparent vote rigging in Sunday's parliamentary elections. The heavy-handed police tactics against journalists and opposition activists are nothing new, nor are the jail sentences based on spurious charges, but there has been a new and slightly surreal backdrop to all this: several thousand young people in white anoraks, waving flags, banging drums and chanting "Putin! Russia!" while opposition activists were being hauled into the back of police vans. They vastly outnumbered the protesters on Monday and Tuesday night in Moscow's Triumphal Square, and, according to some reports, resorted to violence and intimidation to break up the rallies.

They are thought to belong to a group called Nashi (Ours). I spent two weeks filming Nashi for an Unreported World film this autumn. The group was set up in 2005 in response to revolutions in neighbouring ex-Soviet countries to protect against young democratic movements taking power; it has grown to 100,000 members. With seemingly limitless funding and Kremlin backing they were untouchable, but with the Russian opposition movement consumed by infighting, Nashi didn't have a decent sparring partner.

The group had almost become an embarrassment with their over-zealous support for the regime and erotic calendars celebrating Putin's birthday. In a time of relative political stability what exactly were they for?

Outside the American embassy we filmed dozens of Nashi members spray-painting "Forward Russia" on the pavement in 6ft letters. When the notoriously brutal Russian police arrived they were instantly surrounded, filmed and forced to show their documents by members of Nashi. It was clear that the scrawny students, with their powerful political protection, were actually in charge.

Choruses of "I want a man like Putin" sung by beautiful young women accompanied our minibus trips out of Moscow. We started to get a sense this was more of a cult than your average political youth movement. Oksana, a 21-year-old blond, told us artlessly: "I worship Putin. He is a wonderful man, a splendid man, the most worthy politician. I am a fanatic! When he is behind the wheel Russia will be strong. Forward Russia!"

We were invited back to their weekly meeting at Nashi's £20m headquarters in downtown Moscow. The walls were daubed with Putin slogans and 6ft-high murals of his face reminiscent of Soviet-era propaganda. More sinister was the list of potential opposition targets , including young activist, Ilya Yashin, who was this week sentenced to 15 days in prison for his role in the protests. Members also showed us a video of the harassment campaign against opposition leader Boris Nemtsov who the group has clashed with frequently (and who was also detained this week).

Nashi cut their teeth in these skirmishes, and now have a bigger stage on which to exploit their strength.

The members were largely studying in Moscow, but everyone we met grew up in far-flung regions of Russia. Doubtless they were attracted not just by Putin's sex appeal, but by the status and power the organisation could give them, as well as the potential career enhancement in the future – Nashi's founder is now Russia's minister of youth and many of his disciples will follow him into government.

Now the Kremlin's decision to co-opt provincial Russian youth into a mass movement finally looks like paying off. While opposition activists are arrested, beaten and jailed for taking part in protests, the thousands of Nashi members confronting them are seemingly above the law.

But this is no spontaneous show of support. Footage has appeared online of an enormous compound housing thousands of Nashi members who admit to being brought in by bus and by train from as far away as Siberia. There are reports that Nashi members have been given 500 roubles each or even free meals at McDonald's to attend rallies. The Kremlin recognises that sometimes it's better to let eager, young true believers do your dirty work.

One opposition member we spoke to compared Nashi to the Hitler Youth, and while their views are nowhere near as appalling – many are simply young and naive – the certainty in their own righteousness is chilling, and the personality cult around Vladimir Putin is extraordinary.

With talk of the opposition planning another major demonstration on Saturday and more in the weeks to come, it feels like something has changed. The millions of pounds spent turning Nashi into a movement able to call on tens of thousands of state-backed vigilantes suddenly seems like money well spent. Nashi are now an important weapon in the Kremlin's armoury to stifle dissent and could play a crucial role in returning Putin to the presidency next year.