A former England under-21 international midfielder, he started his career at Oxford United in 1991, playing 181 games in five years, helping to send the club on their way back to the First Division in 1995–96 before he signed with Nottingham Forest for a £400,000 fee.
Instead, he was loaned out to Luton Town and Third Division promotion winners Cardiff City, before he was allowed to sign with Port Vale in March 1999.
His career diminished in brief spells with Stockport County and Brighton & Hove Albion before he featured for non-League sides Dover Athletic, Aldershot Town and North Leigh.
He made his debut under Brian Horton in the 1991–92 Second Division campaign; he played fourteen games, helping the "U's" to avoid relegation.
Whilst at Oxford, he was capped twice for England at under-21 level, with both appearances coming in the 1995 edition of the Toulon Tournament, in 2–0 defeats to eventual finalists Brazil and France.
[6][7] He then played 23 Premiership games in 1996–97, and also scored against Ipswich Town in the FA Cup; Forest were relegated at the end of the season.
Allen joined Lennie Lawrence's Luton Town on loan in November 1997 and played seventeen games, scoring once against Bristol Rovers at Kenilworth Road.
[8] He signed with Dover Athletic in October 2001, after manager Gary Bellamy said that he "destroyed the opposition" in the three games he played on trial.
[12][13][14] He was credited as playing a key role in the development of a number of youth team players who made the step up into the Oxford United first-team, including Max Crocombe, Tyrone Marsh, Callum O'Dowda, Josh Ashby, Sam Long and James Roberts.