By Paul Sandle

LONDON (Reuters) - Britain's William Hill has fired Chief Executive James Henderson after only two years in the job because the bookmaker's board said he was failing to deliver enough growth in online and international gambling.

Henderson was promoted from the role of operations director when the highly regarded Ralph Topping retired in 2014. Topping had helped to make the company Britain's largest listed bookmaker by adding online and international operations to its chain of high street betting shops.

The industry faces higher taxes and tighter regulation. A series of mergers among rivals has intensified the competition for William Hill as gambling companies increasingly market themselves to younger sports fans betting via mobile apps.

William Hill said in a brief statement on Thursday that Henderson had left with immediate effect, without giving any details. Speaking to Reuters, Chairman Gareth Davis did not dispute that the CEO had been fired after more than 30 years with the company.

"There remain significant challenges and in the recent past online has not performed in line with our high expectations as a company at the forefront of the market," Davis told Reuters.

Henderson, who received 914,417 pounds ($1.21 million) in salary and benefits in 2015, will be paid 12 month's notice as per his contract but no bonus for 2016, the company said.

Shares in William Hill, which fell to a four-year low of 235.5 pence on June 24, the day after Britain voted to leave the European Union, were trading up 5.3 percent at 290 pence at 1027 GMT on Thursday.

William Hill said its trading remained in line with the previous guidance, with an expectation to produce 260 million - 280 million pounds of operating profit in 2016.

OFF THE PACE

Analyst Gavin Kelleher at Goodbody Stockbrokers said William Hill's online performance had been very disappointing recently.

"In its European online business, amounts wagered have been declining on an underlying basis," he said.

"Their competitor set have got an awful lot better in the last three years and have really raised their game, and William Hill has not been able to match them."

Davis said the strategy of diversifying the business by increasing the share of international and digital revenues remained valid, but Henderson had failed in its execution.

"At a time of increasing consolidation and competition as well as regulatory impacts in our core market, it is key that the delivery of this strategy is accelerated and the board believe this is best led by a new CEO," he said.

Chief Financial Officer Philip Bowcock, who joined in November, had been appointed interim chief executive while a replacement is sought, a process Davis said could take up to 12 months.

"Philip has a clear set of priorities for this transition period, principally the turnaround of the online business," Davis said.

(Editing by Kate Holton and Keith Weir)