* In-play betting is biggest growth area in sports gambling
* Bet365 offers widest range of sports, events
* William Hill offers more possible bets per event
LONDON, Jan 17 (Reuters) - Britain's biggest bookmaker William Hill and family-owned Bet365 are vying for leadership of the fast growing in-play sports betting market, a survey of Europe's online betting firms by industry researcher Gambling Compliance revealed.
In-play betting, which allows gamblers to bet on sporting events while they are taking place, is driving revenue growth across the gambling industry, helping offset stagnant demand for traditional over-the-counter betting.
Bet365, whose television adverts feature the actor Ray Winstone, offered the widest range of sports and events but William Hill offered more possible bets per event, according to the survey, which was conducted in November and December last year.
During the 14-day period of the survey, Bet365 offered in-play betting across 20 sports and 534 events, ahead of Sportingbet on 358, Bwin on 317, Ladbrokes on 313 and William Hill on 297.
However, William Hill was top of the pile in terms of possible bets per event, with an average of 53, well ahead of Ladbrokes on 30, Sportingbet on 25, Bet365 on 24 and Bwin on 23.
Bet365, which has a majority stake in Stoke City football club, is owned by the Coates family. It is chaired by septuagenarian entrepreneur and Labour party donor Peter Coates and run by his accountant daughter Denise.
The survey showed football to be the most popular sport for in-play betting, accounting for over two-thirds of the sporting events on which in-play betting was offered.
Basketball was the second most popular, followed by tennis and volleyball.
(Reporting by Matt Scuffham, Editing by Rosalba O'Brien)