John Tilley has left Sema Group, where he was managing director, to head up outsourcing consultancy Mim Ecom.
Tilley described the parting as "completely amicable" in a letter last week. But his departure has yet to be announced by Sema and it has raised eyebrows among outsourcing experts who are critical of Sema's recent performance in the UK.
Sema, whose UK users include Railtrack, is focusing its efforts on e-commerce and mobile telecoms at a time when a number of key UK contracts are up for renewal.
A five-year Department of Social Security deal is due to expire this month. Earlier this year the two parties were wrangling over changes to any future contract (Computer Weekly, 11 May).
At the end of last year the Government pulled out of negotiations with a Sema-led consortium for a £250m upgrade to the Home Office's IT and telecoms infrastructure.
One outsourcing expert said Sema had failed to establish itself as a credible mid-tier services provider in classic areas such as the desktop.
"They have had a very high staff attrition rate and lost a lot of their bids," he said.