Brought on board to put in place a senior management restructure and develop a new managing team, Allen achieved this earlier this year.
Clarion Events group marketing director Julian Graves said: "Kent had huge influence on the business and how it now operates. As a result of this restructure the role of group managing director no longer fits into the structure."
Clarion Events CEO Simon Kimble added: "Myself and all at Clarion Events wish him the very best for the future."
The company is reponsible for organising events in a number of sectors that range from defence and security to travel and leisure.
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