His frontbench career always promised more than he got the chance to deliver.
After helping to organise Tony Blair's leadership campaign he was given a series of shadow portfolios, including transport and constitution, but in office he never rose higher than government whip.
It may have been his radicalism which prevented his ministerial career rising further.
Mr Allen he is one of Labour's most enthusiastic proponents of constitutional reform, and supports proportional representation for Westminster and a fully elected House of Lords.
He introduced a bill calling for a written constitution in the UK.
In November 2000, he published a book claiming that the UK effectively had a presidency, and that this should be recognised in the constitution.
Mr Allen has also called for the euro to be introduced as a 'dual currency' alongside the pound in the UK.
He was at the forefront of a successful campaign to recall Parliament to discuss Iraq in September 2002, attempting to organise an unofficial recall if the House would not formally sit.
An MP since 1987, he had previously worked for the Labour Party and in local government and trade unionism.
He is an enthusiastic sportsman, and was the first MP to score a century for the Labour cricket team.