The 62-year-old commissioner had already become embroiled in accusations of favouritism and a conflict of interest after he appointed Petra Erler, 48, to her £94,000-a-year job amid reports of a close friendship. He has denied that they are having an affair.

Jose Manuel Barroso, the commission president, defended Verheugen but insiders suggested that behind-the-scenes pressure was mounting for both him and Erler to go.

While accusations of favouritism were denounced by Verheugen, one of Barroso’s vice-presidents and the commissioner for enterprise and industry, as “pure slander”, photographs of the pair holding hands during a two-week seaside holiday in Lithuania last summer have already been splashed across the German press.

Last week Brussels and Berlin joined forces in an attempt to dampen down the publicity, fearful that it would overshadow Germany’s presidency of the European Union, which starts in the new year. But the heat seems certain to intensify if Focus magazine publishes the pictures, which were taken on a nudist beach in August.

Last week Verheugen and Erler were insisting they had done nothing wrong. Ensconced in her commission office late on Friday night, Erler said in a shaky voice: “I’m sure you understand that this is an entirely private matter.”

However, the photographs were shown to a number of German MEPs last week and several of them demanded Verheugen’s resignation.

Focus, whose lawyers were debating whether publishing the photographs would breach Germany’s strict privacy laws, has up to six pictures of the couple naked on a beach. One is said to be of them in the water and another shows them lying in a hollow in the sand. Verheugen is said to be wearing nothing but a white baseball cap.

He was reported yesterday to have instructed a Hamburg lawyer to ensure that the photographs would not be published, citing “invasion of privacy”.

Markus Ferber, a senior member of the parliament’s budget committee, said: “Mr Verheugen says there is nothing between him and the chief of his cabinet. The naked photographs make it clear that that isn’t correct. To protect the reputation of his office he should accept the consequences and resign.”

Verheugen has repeatedly insisted there is no sexual relationship with Erler. “Can’t two adults do as they wish in their private lives?” he reportedly asked.

At the family home in Brühl, south of Bonn, his wife Gabriele remained outwardly unperturbed. “This is old hat,” she said when confronted with the details of the Lithuania trip. “I knew that my husband had this holiday.”

Rumours about Verheugen and Erler began to circulate earlier this year when they were apparently spotted holding hands while wandering through expensive shops on the exclusive Avenue Louise in Brussels, and on another occasion arm in arm holding flowers at a local weekend market.

Journalists began to ask questions after Verheugen appointed Erler, who was already on his staff and likes to dress in black with silver jewellery, to head his office in April. Her salary increased from £6,000 to £7,800 a month.

She also began to act as his gatekeeper. “If you want to get Verheugen to do something, you first have to have Erler on board. He eats out of her hand. Resisting her is pointless,” said an official.

Verheugen first met Erler, a single mother with a daughter, on the political and social circuit in Brandenburg in the late 1990s.

She had already earned a formidable reputation as a high-flyer while state secretary for Europe in the first and only elected East German government. The position brought her into contact with Angela Merkel, the future German chancellor, who was then working as a government press officer.

In 1999, Erler was invited to join Verheugen’s staff and she became one of his most trusted aides. Sources close to Verheugen say it seemed only logical for him to appoint someone who had his complete confidence. “He’s been a little bit naive really,” said the source.

During their Lithuanian holiday, Verheugen and Erler gave an interview to the country’s largest newspaper, Lietuvos Rytas.

“We have had breakfast together and then went to cafes and bars,” Verheugen told the paper. He insisted the trip was perfectly innocent, calling it a “joint meeting during vacation time”.

Frank-Walter Steinmeier, the German foreign minister, sprang to the embattled commissioner’s defence. “There is hardly anyone who knows the EU better than Verheugen, and as a heavyweight in Brussels with us taking over the presidency he is indispensable,” he said.

Merkel has also backed him. Her spokesman said: “The German government shares the European commission’s view . . . that the private life of commissioner Verheugen should be respected.”

If Verheugen were to heed calls for his resignation, it would create a headache for Berlin, with tensions likely in the governing “grand coalition” since the social democrats of the SPD and the conservatives of the CDU would argue over the appointment of a successor.

Explore World News

• Iraq News

• US & Americas News

• Europe News

• Middle East News

• Asia News

• Africa News

Times Recommends

• Earthquake town laid to rest
• Olmert pours cold water on Blair peace push
• Edward Kennedy has brain tumour