Bookmaker William Hill has backed its flourishing online arm by announcing it will spend £424 million on taking full control of the operation.

The swoop on the 29% stake, held by gaming software partner Playtech, came as it posted a 22% rise in pre-tax profits to £292.7m, driven by a third year of online revenues growth above 20%.

Sports betting on mobile phones has been the biggest factor in the latest online improvement, particularly in-play bets in football, basketball and tennis.

William Hill's core business of more than 2300 betting shops also made progress, with operating profits up 7% to £211.5m despite more horse racing fixture cancellations and weak trading during the Olympics.

The value of the retail arm's over-the-counter bets was 1% lower last year, but this was offset by a 5% growth in gaming machine revenues, with an average of £911 per machine left by losing punters each week.

Over the first seven weeks of the new financial year, betting shop revenues jumped by 16% following a favourable run of football results, while online revenue has continued to perform strongly, increasing by 29%.