The officials, Negrão argued, should have been "barred" from having any relations with the company, Galp Energia, which is currently in dispute with the Portuguese state over fines running into millions of euros.

"I would like to add about the prime minister's silence: he can't continue on holiday saying that he won't say anything," said Negrão, who is also chairman of a parliamentary committee on transparency in the exercise of public functions. "He has very special responsibilities in this area. We are talking about ethics in governance."

He said that his party was willing to back a request by another opposition group, the People's Party, that the Socialist government be heard on the matter in the standing committee of parliament.

"These three secretaries of state are barred from any kind of relations with the company Galp," he said. "How is it possible that three members of government in strategic areas and with links to this company could continue to exercise their functions in a situation in which they are in some way compromised?"

"Questions of an ethical nature are only closed when they are completely clarified," he said.

On Thursday the minister of foreign affairs, Augusto Santos Silva, who is minding the shop while the prime minister is on holiday, said that it now saw the matter as closed after the three officials in question have paid back - or promised to pay back - the cost of the trip to France. He announced that a new code of conduct would be introduced to cover such situations.

Negrão countered on Friday that a code of conduct already exists for officials in the tax administration, which is headed by one of the secretaries of state in question, for tax affairs. The secretary of state "has the same obligations" as other tax officials - such as not accepting any gift or hospitality - Negrão argued.

He acknowledged that several deputies from his party may also have accepted corporate invitations to watch Portugal play in France, but stressed that their situation was different from that of members of government.

The secretaries in state in question are Fernando Rocha Andrade, for tax affairs, João Vasconcelos, for industry, and Jorge Costa Oliveira, for internationalisation.