HMRC chief digital and information officer Mark Dearnley (pictured) is to leave the organisation next month when his three-year contract expires.
The departure has been confirmed by HMRC and follows the extension of the mega-outsourcing deals with Accenture and Capgemini. Dearnley was brought in to help oversee their replacement.
Dearnley said in a statement that he had decided to return to the private sector "after three fantastic years to take on a new challenge".
"I joined HMRC with the remit to transform its IT, create new digital services for customers and oversee the smooth transition from the £800m a year Aspire IT contract," he added.
"We have replaced our outdated internal IT, launched digital tax accounts for individuals and businesses, and successfully concluded negotiations to dismantle the Aspire IT contract, taking more direct control of the design and delivery of our digital technology services at huge cost savings for HMRC.
"We have also built one of the strongest digital technology teams in the world, and I am confident that they will continue to deliver HMRC's IT transformation at pace."
However, getting Accenture out of HMRC's data centres before mid-2017, when the contract is up for renewal, may prove a tougher task.
MPs on the Public Accounts Committee had expressed doubts that Dearnley would have the time to prepare HMRC for the planned shift from Accenture and Capgemini to managing multiple smaller contracts with a variety of suppliers by mid-2017.
The announcement last week that the deals will be extended for a further three years indicated that MPs' concerns were not unfounded. The price that the two companies were able to extract in return for the contract extensions has yet to be revealed.
Dearnley's period at HMRC was complicated by the intensification of turf wars in the Civil Service over the future direction and control of IT. The Government Digital Service (GDS) was the focus of the tussles, but outsiders such as Dearnley were caught in the crossfire.
Indeed, GDS co-founder Tom Loosemore, now group director of digital services at the Co-Operative, implied in a series of tweets that Civil Service lifers were out to 'knife' outsiders who had encroached on their turf since the coalition government established the GDS in 2010. Loosemore described it as "a day of the long digital knives".
It also follows the departure of Stephen Foreshew-Cain, executive director at the GDS, and comes as the GDS looks set to be the victim of a power grab by Whitehall mandarins, according to Labour Party deputy leader Tom Watson.
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