Times have changed dramatically since Monsignor Václav Malý endured interrogations, beatings and the indignities of being barred from the priesthood while being forced to clean toilets as the price of campaigning against Czechoslovakia’s communist regime.

As a signatory and then spokesman for Charter 77, a civic initiative demanding respect for human rights that was led by, among others, the dissident playwright Václav Havel, the clergyman was on the frontline of opponents targeted by the hated secret police. Yet this weekend, exactly 30 years after the Velvet Revolution began, ushering in the overthrow of the totalitarian system, Malý – now Roman Catholic auxiliary bishop of Prague – is exhorting a new generation to fight new threats to their hard won freedom.

At a rally at the Czech capital’s Letná field, the same site where he moderated a huge demonstration in November 1989 hailed as a pivotal moment in overthrowing communism, Malý warned a crowd of more than 200,000 that the revolution’s achievements were endangered by politicians who wanted to divide society, limit freedom of speech, and concentrate political and media power in a few hands.

Saturday’s demonstration, organised by the Million Moments for Democracy student movement, was held to celebrate the 30th anniversary of the revolution but also draw attention to what critics contend is a dangerous drift away from its ideals.

It is the latest in a series of protests against the governing style of Andrej Babiš, the country’s billionaire tycoon prime minister, who has been accused of corruption and conflicts of interest, and the role of Miloš Zeman, the populist president who has promoted close ties with Russia and China. Speaking to the Observer in the Prague archdiocese headquarters, adjacent to the city’s magnificent castle, Malý said the pair failed to meet the standards of Havel, who became the first post-communist president of Czechoslovakia and later of the Czech Republic when it split from Slovakia in 1993.

“They change their positions and they are in the hands of PR advisers,” he said. “They give very simple promises that are very dangerous and they speak about enemies and divide society. It is the worst act of their governing.”

It was necessary to commemorate Havel’s ideals – crystallised in his famous quote “truth and love will prevail over lies and hatred” – which, Malý argued, are as relevant today as in communist times. Tributes to the events of 1989 – when Czechoslovakia shook off four decades of communist rule after similar allied regimes had fallen in Poland, Hungary and East Germany – have been ubiquitous in recent days. Slovakia’s president, Zuzana Čaputová, last week laid a wreath at a shrine in Prague’s Národní Třída, where demonstrators were attacked by riot police 30 years ago in an episode that triggered mass street protests heralding the regime’s downfall. Spectacular lighting displays, concerts and other events are planned for Sunday in the Czech capital and elsewhere.

Central to it is Havel, the softly-spoken former dissident who died in 2011 but remains an icon for many liberals.

Václav Havel waves to a crowd of thousands of demonstrators on 10 December 1989 in Prague’s Wenceslas Square, celebrating the communist capitulation. Photograph: Lubomir Kotek/AFP/Getty

Amid the adulation, however, another former Havel ally, Jan Urban, now a professor and political analyst at New York University in Prague, gave a more critical assessment, blaming him for indecisiveness, which bequeathed the Czech Republic unprincipled politicians and an unrepentant communist party that is still in parliament to this day, where it currently props up Babiš’s minority government.

“Václav was superb to the outside world. He put Czechoslovakia back on the map,” said Urban, co-founder of the post-communist Civic Forum movement.

“But domestically he was a disaster. And I say that knowing he was a dear friend. He was a dreamer. He should never have gone into presidential politics and he never learned the rules of parliamentary politics.

“Havel’s time stopped any chance of the fast delegitimisation of the communist party. These civil conflict situations always demand symbolic gestures because people want to believe that the new regime will do its utmost to give society a sense of justice. This was his biggest failing.

“I aways picture a simple comparison; the idea that members of [the Nazi party] would have sat in the West German Bundestag in 1975 is unthinkable. Why is a comparable situation normal here?”

Yet as vivid memories of life under communism resurfaced, Urban, 68, another Charter 77 signatory who was fired as a schoolteacher for refusing to sign official statements denouncing it, tempered his criticism of current developments. “I never expected to see the end of communism,” he said. “I just wanted to inflict as much damage as possible before they got me. So I cannot be disappointed.”

The desire to inflict damage – driven by anger over the loss of an unborn child after his wife miscarried following the trauma of a police interrogation – incurred huge personal strain.

After representing Charter 77 at a human rights conference in Moscow in December 1987, Urban returned to find himself under intense surveillance. Meetings with fellow dissidents had to be restricted to a few minutes or even seconds and convened on bridges, to foil secret police intervention.

In spring 1988, the StB, the communist security service, sent a coffin with his name on it to Urban’s flat in Prague’s Mala Strana district, today a favoured tourist haunt. Anonymous death threats arrived by letter and phone. Determined not to go to jail, he took to sleeping with running shoes beside his bed and a rope by his window to escape any dreaded pre-dawn knock on the door.

Another personal drama arrived in August 1989, when a courier arrived with a letter ordering him to report for military training early next day. Fearing a trick, Urban persuaded a friend to hide him in a hospital emergency ward, under the pretext of a feigned heart attack.

“Two secret police guys showed up and sat in the corridor, demanding that the doctor report everything to do with Mr Urban’s health,’ he said. “Incredibly, there was another Mr Urban slowly dying in the room next door. After five days, hospital staff helped me escape at 5am and I went into hiding for the next 10 days.”

By the eve of revolution, Urban – who was helping to run an underground news agency – was on his last warning. A judge had told him that his next misdemeanour would result in an indictment for subversion which could spell 12 years in jail.When the communist party leadership resigned, a week after protests began, it was “the most joyful few hours of my life”, Urban said.

But there was a catch: “I immediately realised we can do whatever we want – but we didn’t know what we wanted. We were totally unprepared.”