The British Government said it "deplored" Martin Bangemann's behaviour and called for EU rules to be radically overhauled to ensure that no other commissioner could follow suit. Tony Blair is understood to be furious that the German commissioner's decision has tarnished the Commission with yet more allegations of sleaze.
Mr Bangemann triggered outrage among colleagues when he announced on Wednesday he was quitting his job, before the end of his term, for a senior post at the Spanish telecoms giant Telefonica.
As industry and telecoms commissioners, he has been in charge of regulating Europe's telecoms market since 1993 and had extensive dealings with Telefonica and other former state monopolies.
Mr Bangemann wanted to take up his new job yesterday, but he was told by Jacques Santer, the acting commission president, that EU rules barred commissioners from quitting until their post is filled.
However, there are no rules governing perceived conflicts of interest and Mr Blair led calls for a new system aimed at preventing officials from taking private sector appointments immediately after their term of office. In a strongly worded statement, Downing Street made clear the Prime Minister's anger at Mr Bangemann's decision. "The Government deplores what the commissioner has done. This is a time when confidence in European institutions is extremely low and this simply underlines the case for reform," a spokesman said.
The spokesman stressed that it wanted Romano Prodi, the Commission's incoming president, to introduce UK-style restrictions.
Mr Bangemann was left in a state of limbo yesterday after he was told that he could not attend a meeting of the commission executive. He was told he could not represent the Commission at a meeting of industry ministers in Finland today and faces legal action over his decision to quit early.
Most commissioners are expected to stand down on 17 September to make way for a newly formed executive, ordered after the fraud and mismanagement scandal that engulfed Brussels in March.
Telefonica announced that Mr Bangemann was beginning work yesterday but, as far as Brussels was concerned, he was still on its payroll and could not be released.
"He could have avoided all this if he had just waited until 17 September when this team of commissioners stands down," said one commission official. "Doing it this way has just added to the rumour-mill about sleaze and corruption."
Neil Kinnock, one of the UK's commissioners, said he was "flabbergasted" by the job switch, and Pauline Green, Labour MEP and leader of the Socialist group, said the move "reeks of impropriety".
Key decisions about Mr Bangemann's future will now be made by EU ambassadors next week before EU governments agree on an early replacement.
In a formal statement issued yesterday, the Commission expressed "surprise" at Mr Bangemann's job move. It will now be "clarifying" a Treaty of Rome provision, which obliges commissioners to act with "discretion" and "integrity" during and after their terms of office in Brussels.
Leading article, Review, page 3