Allen replaced Lawrie Sanchez in mid-April to oversee the Bees for the third time, but his short-term contract expired after he ensured League Two survival on the final day of last season and Mark Robson, 43, was placed in charge earlier this month.
Assistant manager Guiliano Grazioli and coach Michael Stone, as well as other members of the medical and backroom staff have departed and a club statement read: "Barnet FC can confirm that all of the coaching staff who were in charge of first team matters last season under former manager Lawrie Sanchez have left the club officially.
"The move is another important step by the club in assuring that all members of staff directly associated with the first and youth teams hold the highest coaching qualifications available in football.
"By bringing in the best coaches for the Bees, the aim is to drive the team forward from the Barnet FC Academy upwards and fit in with the club's new footballing philosophy, which was announced early this month.
"All coaches brought in will work under head coach, Mark Robson, and will assist in the coaching of first team players as well as youth team development, in accordance with the new EPPP (Elite Player Performance Plan)."