By Jonathan Davies

The Greek government secretly formulated contingency plans to allow to it to switch from the euro to the drachma at the "flick of a button", former finance minister Yanis Varoufakis has revealed.

Varoufakis told a group of investors in London that Prime Minister Alexis Tsipras instructed him to create a contingency plan in case negotiations over a new bailout deal were unsuccessful.

The former finance minister said he and a five-man team had been working on plans to switch Greece's currency to the drachma for months.

Transcripts of a telephone conservation, which took place a week before Mr Varoufakis resigned as finance minister, were leaked by Greek newspaper Kathimerini.

Varoufakis said: "The Prime Minister, before we won the election in January, had given me the green light to come up with a Plan B. And I assembled a very able team, a small team as it had to be because that had to be kept completely under wraps for obvious reasons."

He admitted that one of his team hacked into the government's own tax office, which was under the control of Greece's international creditors, to obtain reserve accounts and numbers for every taxpayer in the country.

"We decided to hack into my ministry's own software programme," he said.

Speaking to the Telegraph, Varoufakis said the quotes and transcripts were accurate, but claimed some of the Greek reports made it seem as though he and Mr Tsipras had plotted to exit the euro 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.

"It totally distorts my purpose for wanting parallel liquidity. I have always been completely against dismantling the euro because we never know what dark forces that might unleash in Europe," he added.