There were 267 in April and 214 in February, rising from 129 in January.

Gareth Shaw, editor of Which? Money, told Radio 4's Money Box programme: "We have found a third of over 55s have already been contacted about their pension by companies trying to sell them a potentially dodgy product and this has been increasing in recent months."

They found that 2 out of 5 people of those who had been targeted over the last two years had been contacted during the first three months of 2015. The number was double that reported in 2014 as a whole, Mr Shaw said.

He said: "We've seen a real increase in the number of people being called out of the blue about their pensions in the first three months of the year."

Callers typically ring about possible investment opportunities, offering a free pension review, or suggesting there is a legal loophole to exploit.

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Mr Shaw said callers knew the people they were ringing were roughly in the right age group without knowing specific details of an individual's pension.

For many people the calls may have started due to ticking or unticking a box when signing up for a service, possibly years ago, when they may have given consent to something without realising it.

Steve Eckersley, head of enforcement at the Information Commissioner's Office, said that this caused a big problem when trying to prevent the calls. If people have given consent to marketing they have unwittingly opened the door to these calls, he said, though he warned fraudsters that his organisation has stronger powers since last month.

He said: "Prior to April 6, we had to show that consumers had suffered substantial damage or distress.

"But since the change in the law, all we have to show is there has been a serious contravention. We can issue fines up to £500,000. "

He admitted there was "no silver bullet" to bringing scam calls to an end.

But he said the ICO was working hard with other regulators to improve practices in marketing industry.