Was it a cleaner retrieving a stray duster, a secretary in search of a handbag or a senior executive, hell-bent on shredding the evidence?

No one is owning up, but whoever broke the seal placed by European Commission antitrust investigators on an office door at E.ON's premises in Munich has cost the German utility €38 million (£28 million).

The Commission said yesterday that it had imposed the penalty to send “a clear message to all companies that it does not pay to obstruct the Commission's investigations”.

The European Union's sleuths conducted a dawn raid on the E.ON Energie offices in May 2006 as part of an investigation into anticompetitive practices in the German power market.

The seal - a sticker that, when disturbed, displays the word “void” - was placed over a door to protect files that had not been inspected by investigators.

A furious E.ON yesterday denied tampering with the door seal and even suggested that the seal was faulty and past its sell-by date. E.ON said that no documents had been taken from the room and suggested that Commission officials had caused the seal to break when they inspected it the following morning. “E.ON Energie will take all legal measures to contest the fine,” a spokesman said.

The Commission rejected E.ON's argument, suggesting that the explanations provided by the German utility had changed. “First it was the cleaning lady, then it was people moving furniture. A company with the resources of E.ON could have posted a security guard to protect the room,” a spokesman said.

The Commission said it was irrelevant whether the breach of the seal had been accidental as it did not need to prove any intention nor whether any documents had been taken, according to the regulations governing dawn raids.

E.ON is the first company to be fined directly for impeding a Commission antitrust investigation and the fine could have been much higher, up to 1 per cent of turnover, which, in the case of E.ON, could have amounted to €270 million.

Times Recommends

• Equitable Life halts £7bn sale on market turmoil
• Potential buyers emerge to save Woolworths staff
• Terrorist attacks close Bombay Stock Exchange