Mr Livingstone also faces £80,000 costs after the decision by the Adjudication Panel for England after his failure to apologise for the insult a year ago.

The three-man body unanimously ruled that Mr Livingstone had been “unnecessarily insensitive and offensive” to Oliver Finegold, a journalist at the London Evening Standard.

Mr Livingstone said: “This decision strikes at the heart of democracy. Elected politicians should only be able to be removed by the voters or for breaking the law. Three members of a body that no one has ever elected should not be allowed to overturn the votes of millions of Londoners.

“I will meet with my legal representatives early next week and will then make a statement about whether I will be exercising my right of challenge.”

Mr Livingstone was leaving a reception at City Hall when he was approached by the reporter. When Mr Finegold said he was from the Evening Standard, Mr Livingstone said: “What did you do before? Were you a German war criminal?” Mr Finegold replied: “No, I’m Jewish. I wasn’t a German war criminal . . . I’m actually quite offended by that.”

Mr Livingstone added: “Well you might be, but actually you are just like a concentration camp guard. You’re just doing it ’cause you’re paid to, aren’t you? . . . Your paper is a load of scumbags.”

The Board of Deputies of British Jews complained, but the mayor refused to withdraw his remarks.

David Laverick, chairman of the Adjudication Panel, said: “The case tribunal is concerned that the mayor does seem to have failed, from the outset of this case, to have appreciated that his conduct was unacceptable, was a breach of [the Greater London Authority code of conduct] and did damage to the reputation of his office. His representative is quite right in saying . . . that matters should not have got as far as this, but it is the mayor who must take responsibility.”

Jon Benjamin, of the Board of Deputies, said: “The message that one would hope the mayor would take away from this is that he is not the sole arbiter of standards in public life and that an elected official can nevertheless go beyond what is acceptable and can offend people. The right and proper thing to do, and no one would have criticised him had he have done this, would be to make amends and make a proper apology.”

Mr Livingstone’s antipathy towards the Evening Standard, which has campaigned solidly against his mayoralty, has festered for years. To him, it was a justified counter-attack.

An investigation of this kind would be banned under a change in the law proposed by ministers. Phil Woolas, the Local Government Minister, said that public officials should not be investigated if they had not broken the law.

Mr Livingstone was defended by a range of politicians at City Hall, including the Greens and Respect. The Labour MP Diane Abbott said: “Londoners will be shocked and appalled that their mayor can be removed by three unelected members of a quango that nobody has heard of and that is not accountable to anybody.”

If the suspension is carried out as planned from March 1, Nicky Gavron, the deputy mayor, will take over.

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