Traders and hedge funds have bet nearly $8bn (€5.9bn) against the euro, amassing the biggest ever short position in the single currency on fears of a eurozone debt crisis.

Figures from the Chicago Mercantile Exchange, which are often used as a proxy of hedge fund activity, showed investors had increased their positions against the euro to record levels in the week to February 2.

The build-up in net short positions represents more than 40,000 contracts traded against the euro, equivalent to $7.6bn. It suggests investors are losing confidence in the single currency’s ability to withstand any contagion from Greece’s budget problems to other European countries.

Amid growing nervousness in financial markets over whether countries including Spain and Portugal can repair their public finances, Madrid on Monday launched a PR offensive to try to assuage investors’ fears.

Elena Salgado, Spanish finance minister, and José Manuel Campa, her deputy, flew to London to meet bondholders.

They sought to allay doubts about Spain’s creditworthiness by repeating promises to cut its budget deficit to 3 per cent of gross domestic product by 2013 from 11.4 per cent last year. “We’ll make the adjustment that’s necessary,” Mr Campa said. But their disclosure that the treasury planned to raise a net €76.8bn through debt issuance this year unsettled markets further. The projected sum to be raised was lower than the €116.7bn of 2009 but higher than many investors had expected.

The news sent yields on Spanish government bonds, which have an inverse relationship with prices, sharply higher. The premium demanded by investors to hold the country’s debt over German bunds rose to 1 percentage point.

The Spanish government is convinced it is being unfairly treated by foreign investors and the media. José Blanco, Spain’s public works minister, hit out at “financial speculators” for attacking the euro and criticised “apocalyptic commentaries” about Spain’s finances.

Appealing for patriotism, Mr Blanco said in a radio interview: “Nothing that is happening in the world, including the editorials of foreign newspapers, is casual or innocent.”

The single currency fell to an eight-month low of $1.3583 on Friday but recovered a little on Monday to $1.3683. Analysts said sentiment towards the euro had soured because of the increasing concern over Greece’s fiscal problems.

Thomas Stolper, economist at Goldman Sachs, said: ” Behind this intense focus on Greece obviously is the long-standing unresolved issue of how to enforce fiscal discipline in a currency union of sovereign states.”