Millions of people who were mis-sold cover for bank and credit cards are at risk of missing out on redress as a deadline for claiming their money back looms near, consumer help website MoneySavingExpert.com is warning.

The website is urging the financial regulator to extend a cut-off date of August 30, by which time consumers who were mis-sold Card Protection Plan Limited (CPP) card or identity protection insurance products must have submitted their compensation claims.

Around seven million people are eligible for compensation after a redress scheme, which has been running since January, was agreed by 13 banks and credit card companies, through which the insurance was sold, and CPP. The scheme was also ratified by the High Court.

But by June, only around one quarter of those who are eligible had submitted their claims, leaving around five million people yet to do so.

MoneySavingExpert is concerned that many victims of the mis-selling scam have mistaken claim forms they have received as part of the redress scheme for payment protection insurance (PPI) spam, leading them to throw them away.

It has written to the Financial Conduct Authority (FCA) to argue that the deadline should be extended, saying it has heard from people who had initially mistook the CPP letter as PPI junk mail, people who have struggled to get through to an operator on the CPP phone line, and people who do not realise that the scheme is supported by the regulator.

MoneySavingExpert argues that people who have recently moved house may not have had sufficient time to fill in their form. The website said it has offered to help draft a follow-up letter.

The FCA said that the August 30 cut-off date was clearly set out in letters sent to consumers and that this date was approved by the High Court as well as CPP customers themselves.

Martin Lewis, founder of MoneySavingExpert.com said: "Seven million people who've had debit or credit cards since 2005 have been sent what are effectively 'fill this in to get your money back' letters from CPP.

"But because people are so used to seeing spam about PPI, the inadvertently similar name means up to five million people may have binned letters.

"This is particularly an issue for vulnerable people that don't have access to the online help to check whether the letters are legit.

"If the FCA doesn't send new letters and extend the deadline, the banks and CPP will simply get to keep the money and will have gotten away with it."

The website said people it has heard from who almost did not bother reclaiming include a woman named Angela, who said: "Threw it away, then heard your advice and retrieved it, received over £200."

Another woman, named Caroline, told the website: "Phoned up for replacement CPP forms, I did think it was junk mail when they arrived 1st time."

CPP was fined £10.5 million in November 2012 after regulators found it gave misleading and unclear information about credit card and identity theft insurance.

The mis-selling scandal ran from 2005 to 2011, although only a proportion of the policies sold were arranged directly through CPP.

Many customers were sent new bank cards which they had to activate by going through a CPP call centre, where they were offered insurance.

They were persuaded to spend £30 a year to insure their card, or around £80 for an identity protection policy - despite many already having cover provided by their bank or credit card firm.

Towards the end of last month, the FCA sounded an alert for people not to delay filling in and returning their compensation claim forms and recommended that they post off their completed forms "well before" the end of August.

The average sum people have received so far in redress is £188.

The FCA said in a statement that its "primary goal throughout" has been to ensure that CPP customers get fair redress via a quick and simple process.

The statement said that the redress scheme was set up by the scheme administrator and the FCA gave its input to ensure that the process was fair.

It continued: " The 30 August cut-off date was a feature of the scheme that was approved by the High Court and also CPP customers in a vote last year.

"The FCA supported this cut-off date and made sure it was given prominence in the letters sent to customers. More recently, in July we issued a reminder encouraging people not to delay so they don't miss out.

"It is for the scheme administrator to decide whether there is an extension to the deadline and any change to the scheme will need to be agreed by all participating members.

"Meanwhile, there is still time for people to claim, so - if they wish to do so - they mustn't delay."

MoneySavingExpert said it has not heard of anyone who was sent a reclaim letter who has been refused their money back.

It said that anyone who believes they have been affected can call 08000 83 43 93 or get help with reclaiming by visiting www.moneysavingexpert.com/CPPreclaim.