In a prepared statement sent to Research today, Sparrow said: “In July last year we completed the sale of ICM and it became a fully-owned subsidiary of Creston. I came to the view that a new chapter should open for me as well and hence tendered my resignation.”

Sparrow is currently signed-off sick. He is set to leave the company officially by early August. Widely known for his political polling work, it is not clear at this stage whether Sparrow will return to work in time to lead ICM’s voter research in the run-up to the UK general election, which is due to be held on or before 3 June.

Before setting up ICM in 1989, Sparrow was managing director of Marplan. He also worked as a private pollster to Conservative Party Central Office between 1995 and 2004.

Creston CEO Don Elgie said: “Under Nick’s leadership, ICM has become one of the premier research agencies in the UK with a diverse mix of blue chip clients and expertise. He has also brought together a strong management team with considerable depth and breadth of talent and experience. I am extremely proud of everything that Nick and this team have achieved and am delighted that the company continues to flourish under the ownership of Creston.”

Speaking to Research, Elgie said it was too early to say who would replace Sparrow either as chairman of ICM or as head of Creston’s insight division, which also includes the agency Marketing Sciences.