On 23 July 2004, the Member of Parliament for Hartlepool, in England, Peter Mandelson (Labour), was nominated as the United Kingdom's new European Commissioner for Trade. On 8 September, he accepted the office of Steward of the Manor of Northstead, thereby disqualifying himself from Parliament, and causing a by-election. Polling took place on 30 September.

Peter Benjamin Mandelson, Baron Mandelson, is a British Labour Party politician who served as First Secretary of State from 2009 to 2010. He was President of the Board of Trade in 1998 and from 2008 to 2010. He is the president of international think tank Policy Network, honorary president of the Great Britain–China Centre, and chairman of strategic advisory firm Global Counsel. Mandelson is often referred to as a Blairite.