Companies who break the rules will be fined up to £250,000, up from the previous maximum of £100,000, E-commerce Minister Alun Michael said.

The rise comes after a review by communications watchdog Ofcom.

Consumers were concerned by the risk of unknowingly being connected to expensive internet diallers.

Hefty bills

There had also been a surge in phone text promotions prompting callers to dial premium rate numbers.

The fine increase was also backed by Icstis, which regulates premium rate calls.

Mr Michael said: "We all have the right to use the internet without the fear of being exploited by firms who prey on consumers.

"Customers have unwittingly run up hefty phone bills when their automatic dial ups get locked in to a premium rate number.

"I want to see an end to that."

Icstis director George Kidd said the £100,000 fine limit was "no longer sufficient to deal with the worst services we see."

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"A new fine limit, combined with the other proposals in the Ofcom review to strengthen consumer protection, should ensure that the relatively small number of rogues out there do not continue to damage trust and confidence in the entire premium rate industry."

Crazy Frog

Separately, Icstis said it had received more than 100 complaints about companies behind the Crazy Frog ring tone.

Complaints have come from people who say they unwittingly signed up for a subscription ring tone service thinking they were only making a one-off payment.

Icstis will examine whether mBlox, which provides a premium-rate number service to Jamster, which markets the ring tones, is in breach of the industry's code of practice.