He has made it clear to Downing Street that he is willing to risk his career in the most unpredictable political battle for years.
His move comes days before Tony Blair's second cabinet shake-up of the year, when he names a replacement for Lord Robertson as defence secretary. Although Mr Dobson, MP for Holborn and St Pancras and former leader of Camden LBC, has said repeatedly he does not want to leave his department, he has come under pressure from friends and admirers to stand in London. Moreover, Downing Street believes he has the stature to beat Mr Livingstone, Labour's front runner.
Local government and housing minister Nick Raynsford, who has ministerial responsibility for London, threw his hat into the ring last week, but No 10 believes he and Gelnda Jackson, another declared candidate, are not heavyweight enough to win.
Then, Lord Archer, the newly-chosen Conservative candidate would stand a good chance of winning executive control of the capital.