Allen is a former West Ham United trainee who also played for Tottenham Hotspur at youth level. He moved to Birmingham City during 2005. He scored 13 goals in 18 games for Birmingham's reserves, but never played for the first team, moving to Barnet on a free transfer in January 2007.[3] He had some success at Barnet, scoring four goals in four consecutive games in February, but did not add to that tally, and was released by the club in May 2007.[4]
After impressing on trial – scoring a goal against Tottenham Hotspur in a friendly[5] – Allen signed a two-year contract with Conference National side Stevenage Borough.[6] In February 2008, he went on loan to Crawley Town.[7] At the end of the 2007–08 season he retired from football due to a persistent knee injury and the remainder of his contract was cancelled by Stevenage.[8]