The rise of anti-austerity parties in Greece and Spain is “good news for Europe”, the economist Thomas Piketty has said, adding that citizens are paying the price of “incredible” attempts to force southern European countries to pay off their debts too fast.

“The French far right is much more dangerous than Syriza or Podemos, which are pro-European parties that want to build a different Europe,” author of the best-selling Capital in the Twenty-First Century said in a TV interview with Pablo Iglesias, founding leader of Spain’s new party Podemos, to be screened on 18 January.

“You can argue that, in Syriza’s case, their policies are not as clear as they might be, but you have to offer them support because they want to build a democratic Europe, which is what we all need.”

Podemos has shot to political prominence in Spain since it was founded nine months ago, allying itself with the anti-austerity stance of Syriza in Greece.

With Greece’s general election just two weeks away, the incumbent prime minister Antonis Samaras’s New Democracy party continues to trail Syriza in polls by 2-3 percentage points. Samaras sought to counter the leftists’ appeal at the weekend with a personal pledge that Greeks would suffer no more pension or wage cuts.

In the hour-long TV interview, Piketty described austerity policies as “a failure” and supported the Podemos agenda of a basic income for those most affected by the crisis as well as restructuring debt, a policy that has been heavily criticised by Spain’s hitherto dominant parties, the Socialists and the Partido Popular.

He pointed out that at the end of the second world war France and Germany’s debt was 200% of GDP, “when there was no such thing as public debt”. “It’s incredible,” Piketty said. “It’s an act of historical amnesia to tell southern European countries that they have to pay all their debt, down to the last cent, with zero inflation.”

The economist believes that European countries have tried to get rid of their deficits too quickly. The result is that “their citizens have suffered the consequences in the shape of austerity policies. It’s good to reduce deficits, but at a rate that’s commensurate with growth and economic recovery, but here growth has been killed off.”

Last week Piketty poured cold water on the Spanish government’s claims that the crisis was over and insisted the eurozone still faced the risk of stagnation, weak growth and negative inflation.

During the interview, he advocated a common European economic policy with a strong parliament overseeing the work of the European Central Bank. Were countries such as France, Italy and Spain to propose the creation of “a real European parliament”, Germany would have no option but to go along with it, he said.

The meteoric rise of Podemos – or We Can – has taken Spain’s political class by surprise. The main parties have resorted to sniping and ridicule, which have merely served to win the party more support from a public tired of cronyism and corruption.

According to a poll published on Sunday in El País newspaper, Podemos would win were a general election held tomorrow. The elections are due in December but the shakeup of the old political order is set to begin in May when municipal elections are scheduled in key cities such as Madrid and Barcelona.

Iglesias said Piketty had agreed to act as an informal economic policy adviser to Podemos.