An investigation has been launched into claims millions of people's pension pot details are being sold and ending up in the hands of criminals.

Pensioners' salaries, the value of their investments and the size of their pensions are being sold for as little as 5p without their consent, the Daily Mail reports.

The financial details are allegedly being bought by fraudsters and cold-calling firms.

The paper reports that its undercover reporters were sold pension pot details for 15,000 people without any checks being made on who they were and what they wanted the data for.

The Information Commissioner's Office (ICO), the privacy watchdog, has launched an investigation into the claims and said it would be speaking to the Pensions Regulator, the Financial Conduct Authority and police.

The probe comes ahead of next week's pension reforms, which will give Britons the chance to access their full retirement pots.

Experts at the ICO have previously warned that the pension reforms on April 6 could result in a flood of scams on the scale of "the next PPI scandal".

Steve Eckersley, the head of enforcement at the ICO, said the revelations are "very worrying indeed".

He said: "It suggests a frequent disregard of laws that are in place specifically to protect consumers. We will be launching an investigation immediately.

"We're aware of allegations raised against several companies involved in the cold-calling sector, and will be making inquiries to establish whether there have been any breaches of the Data Protection Act or Privacy and Electronic Communications Regulations.

"The ICO has powers to issue companies with fines of up to £500,000 for the most serious breaches of the Data Protection Act, while we can also pursue criminal prosecutions around unlawfully obtaining or accessing personal data."

An ICO spokesman said it appeared that some firms were getting their hands on pension details because some people do not read the terms and conditions of contracts they sign, leaving them open to having their personal data accessed.

However, he said that it appeared some companies were getting and selling on the information unlawfully.

Some details appear to have been stolen, while other firms appear to have kept personal information when they should have deleted it.

Discussing the pension reforms, Mr Eckersley added: "The information we've been shown supports the work we've been doing to target the shady industry that operates behind the nuisance of cold calls and spam texts.

"We're already aware of the potential for a huge spike in the number of scam texts and calls linked to pensions when the law changes in April, and have already taken action against a company that was sending out misleading messages.

"What we've seen here confirms those fears. Personal data is such a valuable asset, particularly financial information.

"The worst case scenario here is this information getting into the wrong hands and being used to target individuals at a critical point in their financial lives.

"We'll be speaking to the Pensions Regulator, the Financial Conduct Authority and the police about the information the Daily Mail has shown us."

Shadow work and pensions secretary Rachel Reeves said: "Today's revelations that personal data is being passed on to those looking to make a quick buck out of pensioners' savings are shocking.

"This is further evidence of the Government's total failure to protect more than 300,000 savers who could start accessing their pensions in just over a week's time.

"Ministers have ignored warning after warning about the threats to savers from fraudsters, but they must now act quickly to protect savers from these serious threats to people's hard earned retirement income.

"Labour supports greater flexibility on retirement, and will take swift action to protect savers, with a cross-government task force to stamp out scams, and caps on pension fees and charges, including for retirement products, so that savers get the most out of their money."