* Ban follows government review launched last year
* 22% of online gamblers are 'problem gamblers' - commission
* Betting companies' shares fall (Adds details)
LONDON, Jan 14 (Reuters) - Britain's 24 million adult gamblers will not be able to use credit cards to make bets under a new rule designed to prevent consumers from building up too much debt, sending shares in betting companies sharply lower.
The Gambling Commission said on Tuesday the ban, which comes into effect on April 14, will apply to all online and offline gambling products apart from over-the-counter lottery tickets.
Research by the commission classes 22% of online gamblers who use credit cards as "problem gamblers".
The move follows a government overview of the industry launched in November which was aimed at overhauling online casinos, including a ban on using credit cards for gambling online aimed at vulnerable people.
"Credit card gambling can lead to significant financial harm. The ban that we have announced today should minimise the risks of harm to consumers from gambling with money they do not have," said Neil McArthur, Gambling Commission chief executive.
British betting companies are also struggling with the government's clampdown on high-speed slot machines, which critics have called the "crack cocaine" of gambling.
At 0835 GMT, 888 Holdings shares were down 3.5% at their lowest since August, Flutter Entertainment shares were down 1.2% and William Hill was down 2.5%.
Of Britain's estimated 24 million adult gamblers, around 10.5 million gamble online, the commission said. UK Finance estimates around 800,000 Britons use credit cards to gamble. (Reporting by Elizabeth Howcroft and Josephine Mason; editing by Kate Holton and Mark Potter)