UK bookmaker shares have fallen after Prime Minister David Cameron voiced concerns about high-stakes "crack cocaine" gambling machines in betting shops.

Cameron, speaking during Prime Minister's Questions in the House of Commons, told parliament that fixed-odds betting terminals were a "problem".

The machines, which enable gamblers to spend up to £300 ($493, €363) in a minute and are allegedly highly addictive, have been dubbed the "crack cocaine" of Britain's high streets.

The Gambling Commission estimated there are more than 33,000 of these machines in betting shops - generating over £1.5bn a year in revenue.

But Cameron said the government would wait for a report expected to come before parliament early this year before taking action.

The Prime Minister's indication of possible action drove shares in William Hill and Ladbrokes down in early Thursday trading.

William Hill shares were down 5.7% at 376.89p pence at 10:01 while shares in Ladbrokes, Britain's second biggest betting company, fell 5% to 170.58p.

Ed Miliband, the leader of the Labour Party, previously pledged that he would legislate to put betting shops in a separate use class so that councils can use planning powers to control the number of FOBTs opening in their area.

"In town and cities across Britain today, you can see how the old bookies are being turned into mini casinos," Miliband said.

He added: "In the poorest areas, these are spreading like an epidemic along high streets with the pawn shops and pay day lenders that are becoming symbols of Britain's cost-of-living crisis.

"The time has come to give local communities the right to pull the plug on these machines - the right to decide if they want their high streets to be the place for high stakes, high speed, high cost gambling."

The Labour leader also pledged to legislate to reduce the harm caused by these machines by increasing the time between plays, requiring pop-ups and breaks in play.