The Japanese Minister of Finance, Shoichi Nakagawa, has blamed a heavy dose of cold medicine for a slurred and baffling performance at the G7 meeting in Rome, where the man at the helm of the second-biggest economy in the world appeared to be drunk.

Mr Nakagawa claimed to have taken only a few sips of wine – “no more than a glassful” – before the news conference but he seemed too addled to state correctly the current level of Japanese interest rates.

Upon his return to Japan today the Finance Minister was greeted with immediate calls for his resignation by opposition MPs, who said that the affair was an embarrassment to the country and a shame that sent a “message to the whole world”. His embarrassment was compounded yesterday by the revelation that under Mr Nakagama’s stewardship the Japanese economy had nosedived and was now faring worse than at any time in the past 35 years.

Late last night the main opposition Democratic Party of Japan agreed on a censure motion against Mr Nakagawa in the Upper House of parliament. If successful, the vote could force Mr Nakagawa from his post less than six months after he took on the role.

Yukio Hatoyama, the secretary-general of the Democratic Party, said: “I think he should be fired immediately. He has damaged the national interest.”

Mr Nakagawa said that he had drunk alcohol during his flight to Rome and had taken some cold medicine – a combination, he said, that may have affected him adversely. He insisted that his performance would not affect Japan’s standing among the other G7 members.

The worst excerpts of his 20-minute press conference were swiftly uploaded to the internet and quickly became the most-watched video on YouTube in Japan.

“I feel terribly sorry for the Japanese public as well as the Diet [parliament] that such footage and words of mine were conveyed to the world,” said Mr Nakagawa in an apology to a parliamentary panel yesterday.

Medical experts suggested that the excuse may have some truth to it because Japanese cough mixture does contain codeine.

Because of Mr Nakagawa’s closeness to Taro Aso, the Prime Minister, the incident provides an increasingly confident opposition with yet more ammunition to use against the embattled Government. The Liberal Democratic Party has come under intense public criticism for its lacklustre handling of the economic crisis, with Mr Nakagawa bearing the lion’s share of the blame for failing to come up with a more comprehensive rescue package.

Public support for Mr Aso’s Cabinet now stands at below 10 per cent – a level that has historically forced Japanese prime ministers to resign.

At the press conference in Rome Mr Nakagawa seemed barely able to keep his eyes open and mistakenly answered a question directed, by name, to the governor of the Bank of Japan sitting next to him. His answers frequently trailed off into incoherent mumbling. At one point he said that Japan had pledged $1 billion (£695 million) to the Asian Development Bank, which it has not.

He might, some suggested generously, have been thinking of the $100 billion in loans pledged to the International Monetary Fund.

Mr Nakagawa’s performance was condemned by his party colleague and former Prime Minister Yoshiro Mori, who said: “Since he really loves to drink, I advised him once to be careful about drinking.”

Yasunaga Matsuki, a press officer working in Mr Nakagawa’s office, toldThe Times that he did not think he had ever seen the minister drunk while at work and did not know of him keeping alcohol in the office. He did, however, say that Mr Nakagawa had “suffered from a cold a few times before”.

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