Sky News has learnt that Ken Hanna, who has chaired The Restaurant Group (TRG) since the beginning of last year, has informed boardroom colleagues of his intention to step down once a successor is identified.

In addition to Wagamama, TRG owns chains such as Chiquito's and Frankie & Benny's.

The departure of Mr Hanna, a respected City figure who has chaired companies including Aggreko and Inchcape, could be announced as early as Friday.

His plan to exit is understood to have been motivated by a desire to enable Andy Hornby, TRG's chief executive, and colleagues to focus on steering the company through a challenging economic environment.

Oasis Management, a Hong Kong-based activist fund, owns nearly 15% of the restaurant operator, and has been vocal in demanding a board seat and a number of directors to step down.

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"Ken clearly wants to avoid a prolonged and distracting dispute with Oasis when the company's just reported a sector-leading set of results and another [profit] upgrade," said a person close to the company.

Earlier this week, TRG said it had enjoyed strong sales growth in the half-year to 2 July, and that it was making good progress in cutting its debt pile and improving margins.

Jason Molins, an analyst at Goodbody, described the statement as "another reassuring update from the group", while Douglas Jack at Peel Hunt wrote: "Our view is that the greatest value will be realised by allowing the company more time to rebuild profitability."

On Thursday, shares in TRG closed up nearly 4% at 44.2p, giving it a market value of £334m.

A spokesman for TRG declined to comment.