 At the 1918 general election, Colfox was elected as Member of Parliament (MP) for Dorset North as a Coalition Unionist (majority 212) becoming in 1920 Private
Secretary (unpaid) to Parliamentary Secretary to the Ministry of Pensions (George Tryon) and in 1921 Private Secretary (unpaid) to Parliamentary Under-Secretary of State for the Colonies (Hon EFL Wood - Lord Halifax).At the 1922 general election, he was returned to the House of Commons as MP for Dorset West with a majority of 4,548.Between 1922-3 he was Assistant Government Whip.