A Sussex MP quit his job as a government aide as the war in Iraq got under way.
Hastings and Rye Labour MP Michael Foster said the Government had the legality for war but not the legitimacy.
He defied the whip by not voting with the Government in the debate on military action, where more than 100 Labour backbenchers revolted.
Labour rebels included Brighton Pavilion MP David Lepper and Brighton Kemp Town MP Des Turner.
Lawyer Mr Foster abstained from voting.
He has now quit as Parliamentary Private Secretary to the Attorney-General, Lord Goldsmith, a role he has held for more than three years.
Mr Foster said today: "I simply couldn't support the Government at this time, while the weapons inspectors continued to believe there was at least a hope of a peaceful resolution."
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