The advisory firm at which George Osborne, the former chancellor, is a partner, has landed a key role on the $75bn takeover of Activision Blizzard by Microsoft.

Sky News has learnt that Robey Warshaw, which was set up by the British investment bankers Sir Simon Robey and Simon Warshaw, has been enlisted as an adviser to Call of Duty-maker Activision.

City sources said the firm, which Mr Osborne joined as a partner in 2021, had been involved in the takeover for some time, although its role has not been publicly disclosed.

The deal has become engulfed in controversy after the Competition and Markets Authority’s (CMA) decision to block it.

Regulators elsewhere have approved it, with Microsoft pledging a string of licensing concessions involving rival gaming platforms, prompting the technology behemoth to accuse the UK of stymying innovation.

Brad Smith, the Microsoft president, met the chancellor, Jeremy Hunt, earlier this week to protest at the CMA’s stance.

Mr Smith has questioned Britain’s attractiveness as an investment destination in light of the decision.

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It has now formally appealed against the verdict, while the two companies have enlisted legal heavyweights including Lord Pannick KC to argue their case.

A resolution overseen by the Competition Appeal Tribunal is likely to take several months.

Robey Warshaw declined to comment, while Activision could not be reached for comment.

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