Some members of Greece’s leftist-led government wanted to raid central bank reserves and hack taxpayer accounts to prepare a return to the drachma, according to reports that highlighted the chaos in the ruling Syriza party.

It is not clear how seriously the government considered the plans, attributed to former energy minister Panagiotis Lafazanis and ex-finance minister Yanis Varoufakis. Lafazanis was sacked from his post and Varoufakis resigned earlier this month. However, the revelations have been seized on by opposition parties who are demanding an explanation.

The reports on Sunday came at the end of a week of fevered speculation over what Syriza hardliners had in mind as an alternative to the tough bailout terms Tsipras has reluctantly accepted to keep Greece in the eurozone.

About a quarter of the party’s 149 MPs rebelled over proposals to pass sweeping austerity measures in exchange for up to €86bn (£60bn) in fresh loans. Tsipras has been struggling to hold the party together.

In an interview with Sunday’s edition of the RealNews daily, Lafazanis said he had urged the government to tap the reserves of the Bank of Greece in defiance of the European Central Bank.

Lafazanis, the leader of a hardline Syriza faction that has argued for a return to the drachma, said the move would have allowed pensions and public sector wages to be paid if Greece were forced out of the euro.

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“The main reason for that was for the Greek economy and Greek people to survive, which is the utmost duty every government has under the constitution,” he said.

In a separate report in the conservative Kathimerini newspaper, Varoufakis was quoted as saying that a small team in Syriza had prepared plans to secretly copy online tax codes. It said the “plan B” was devised to allow the government to introduce a parallel payment system if the banks were closed down.

In remarks which the newspaper said were made at an investors’ conference on 16 July, Varoufakis said passwords used by Greeks to access their online tax accounts were to have been duplicated secretly and used to issue new pin numbers for every taxpayer to be used in transactions with the state.

“This would have created a parallel banking system, which would have given us some breathing space, while the banks would have been shut due to the ECB’s aggressive policy,” Varoufakis was quoted as saying.

Varoufakis stood down this month to facilitate bailout talks. He has been a strident opponent of the deal ever since.

Under the secret plan, which the report said was devised before Tsipras was elected in January, transactions through the parallel system would have been nominated in euros but could easily change into drachmas overnight.

Varoufakis told the Daily Telegraph that the quotes were accurate but some reports in the Greek press had been twisted, making it look as if he had been plotting a return to the drachma from the start.

“The context of all this is that they want to present me as a rogue finance minister and have me indicted for treason. It is all part of an attempt to annul the first five months of this government and put it in the dustbin of history,” he said.

The deputy finance minister Dimitris Mardas denied the government had ever discussed plans to take Greece out of the euro. “I have repeatedly said that such discussions have never taken place at a government policy level,” he told SKAI television.