Alan contested Barnsley West and Penistone in the 1987 General Election and was elected for Rutland and Melton in 1992 and re-elected in 1997, 2001 and 2005.
He served on the Social Security Select Committee 1993-95 and was Charmain of the Conservative Backbench Constitutional Affairs Committee 1994-95.
In July 1995, he was appointed Parliamentary Private Secretary to the Rt Hon Dr Brian Mawhinney MP, Charmain of the Conservative Party.
In June 1997 he was appointed Vice-Chairman of the Conservative Party, and Parliamentary Political Secretary to the Leader of the Party, the Rt Hon William Hague MP.
In June 1998, Mr. Duncan was appointed Shadow Health Minister. And in June 1999, he was appointed Shadow Trade and Industry Spokesman.
In 2001 Iain Duncan Smith appointed Alan as Shadow Foreign Minister with special responsibility for the Middle East. In 2003 he was promoted to Shadow Secretary of State for Constitutional Affairs and in 2004 he was appointed Shadow Secretary of State for International Development. After the 2005 General Electionm Mr Duncan was promoted to the Shadow Cabinet as Shadow Secretary of State for Transport. In December 2005, David Cameron appointed Alan as Shadow Secretary of State for Trade, Industry & Energy.