He was the man who saved Hugo Chávez when all seemed lost. A coup had ousted Venezuela's president and buried, it seemed, his leftist experiment.

General Raúl Baduel, however, stayed loyal and tilted the army Chávez's way during tumultuous days in April 2002, paving the way for his triumphant return to power and restoring democracy. A grateful Chávez hailed the general a hero and appointed him defence minister. They became close allies and confidants.

Times change. Baduel is now stripped of power and facing corruption charges that could keep him in jail for decades. Prosecutors say he pilfered state funds. Baduel says his crime was to realise – and declare – that the president was a tyrant.

"Every day there is more repression, and Chávez's mask slips further. The only thing Chávez cares about is being president for life," he said, seated at a desk in his cell. "This," he said, tapping a pile of legal documents emblazoned with his name, "is a judicial farce".

Since April the general has been kept behind three layers of guards and gates at a hilltop military jail in Los Teques, outside Caracas. He has been accused of corruption over £8m which allegedly disappeared during his tenure in government, a charge levelled after he broke with Chávez and joined opposition ranks.

Baduel is not alone. Criminal charges are multiplying against government opponents. Some are accused of corruption, others of public disorder during demonstrations. Some are in exile, others in jail pending trial.

Critics say the president has become authoritarian and is using courts to neutralise foes. "Given the way Chávez and his supporters have undermined the independence of the judiciary it is difficult to have confidence in the fairness of the trials," said Daniel Wilkinson, of Human Rights Watch.

A tougher approach is already on display. Police, citing disorder, use teargas to break up demonstrations and jail organisers. Twelve municipal workers were arrested during a protest over working conditions.

In the western state of Táchira an opposition governor, César Pérez Vivas, was charged after leading a rally that ended in scuffles with government supporters.

"These charges are a tactic to intimidate and discourage people from protesting," said Jackeline Sandoval, of Fundepro, a human rights watchdog. By the group's count there are 38 people in jail for political reasons disguised as corruption or public disorder offences.

Some choose to flee. Manuel Rosales, an opposition leader and former presidential candidate, is among half a dozen exiles who have sought political asylum in Peru.

Criminal charges, along with blacklisting opposition candidates, usurping municipal power and closing 32 radio stations, mark a new phase in Chávez's decade-old rule, said one senior European diplomat. "We've gone from calling Venezuela an imperfect democracy to an authoritarian regime with democratic characteristics," he said.

Former US president Jimmy Carter, who has praised Chávez's pro-poor policies and endorsed his electoral victories, recently voiced concern at an authoritarian drift. The government declined a request for an interview but has publicly rejected such criticisms as unfair. Chávez has won successive elections and remains popular. He is a hero in the slums for spending oil revenue on social programmes.

Opposition parties organise freely and opposition newspapers and TV stations display shrill partisanship which makes Fox TV look tame. Government supporters say the same elitist, anti-democratic forces that briefly ousted Chávez in 2002 – a coup endorsed by the Bush administration – are again plotting his overthrow.

"I think that behind these mobilisations there are dark forces," Reinaldo Garcia, head of the national assembly's human rights commission, told the state news agency ABN. "We cannot allow them to block the streets and highways, much less burn tyres at strategic spots to provoke problems with the security forces."

The attorney general, Luisa Ortega, a Chávez ally, said demonstrators who sought to destabilise the government would be charged with "civil rebellion", which carries 12 to 24 years in jail. "I would like such people … to know what the consequences will be."

Steve Ellner, a historian and analyst at Venezuela's University of the East, said intense polarisation led both sides to overreact but that Chávez remained a democrat, not least because of electoral mandates. Ellner He noted however that courts overwhelmingly targeted opposition figures. "Chávez's case would be much stronger if he went after corruption within his own government."

Arresting Baduel neutralised an opponent who could stir trouble in the army. "Obviously throwing Baduel in jail had a political motivation."

Since his arrest the general has been kept in a military prison outside the capital. Denied access to telephones or the internet, Baduel is a forlorn figure whose call for an assembly to rewrite the constitution and rein in the president is largely unheard.

In the 1980s Baduel and Chávez were part of a secret cell of young army officers who plotted to seize power and usher in "real" democracy, but the president had betrayed that promise, said Baduel. "We are in a new modality of dictatorship which has a facade of democracy." The former defence minister, an authority on eastern religions, spends his days meditating, reading, writing and blending fruit juices. He used to share his cell with a former navy admiral and a former national guard general who were accused of plotting to kill Chávez. The charges were dropped and they were released last week.

Baduel does not expect to be a free man soon. "I know I will leave this prison only when Chávez leaves the presidency of Venezuela."

Opponents

Raúl Baduel Former defence minister who broke with Chávez, arrested in April on corruption charges. Trial started today.

Manuel Rosales Mayor of Maracaibo and former presidential candidate, charged with corruption. Fled to Peru in April.

Oscar Pérez Founder of anti-Chávez group, charged with inciting violence during demonstration against education law. Fled to Peru in August.

Richard Blanco Prefect of Caracas, arrested with 11 municipal workers while protesting at working conditions. Accused of damaging police barriers.

Didalco Bolívar Former governor, who refused to join Chávez's party, charged with corruption. Fled to Peru in August.

Leopoldo Lóez Opposition leader and former mayor of Chacao, one of several hundred mostly opposition candidates banned from elections while corruption allegations investigated.