Government CIO John Suffolk has announced he is to leave his £270,000 a year job at the end of the year.
His role, considered one of the most influential in UK IT, will be filled temporarily by COO of the Efficiency and Reform Group, Ian Watmore, while a replacement is sought.
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Under Gordon Brown's government, Suffolk was instrumental in setting up the government's G-cloud strategy, and more recently called for more transparency in government IT services procurement and encouraged Indian IT service providers to bid for large contracts.
However, following the election he had been the subject of rumours that he would step down rather than continue to serve under the Conservative Liberal Democrat coalition.
In a statement, Suffolk said: "Without doubt we have transformed the UK into a leading user of technology benefiting citizens and the UK economy."
"I am immensely proud of the way we have supported the new coalition government in its first six months and have greatly enjoyed working with Francis Maude and his team," he said.
According to Tola Sargeant of TechMarketView, his replacement is likely to be a close ally of Watmore.
Said Sargeant: "Suffolk has achieved a lot in relatively a short space of time, most recently playing a key role in contract renegotiations with IT suppliers enforcing the ICT moratorium and carrying out project reviews.
"Whoever fills his shoes will have to be an equally strong character if they are to keep this momentum and force through the changes required to achieve the government's savings targets and dramatic improvements in public sector efficiency," she added.
Suffolk has held the post since 2006, prior to which he directed the transformation of the criminal justice system's IT for the Home Office.