A banking group has been taking hundreds of complaints a day from customers who are upset at being charged high and unexpected fees by payday loan middlemen.

RBS, which also owns the NatWest and Ulster Bank brands, has been receiving as many as 640 calls a day from vulnerable consumers about attempts to charge fees on their accounts.

It has seen more than one million attempts made by payday loan brokers to claw money out of people’s accounts in the space of just one month.

RBS said it is working with regulators and other organisations to put unscrupulous payday brokers, which charge borrowers a fee to potentially find them a deal, out of action.

Often, the person looking for a payday loan wrongly assumes that the middleman is a lender. The financial ombudsman has also seen large volumes of complaints about payday loan middlemen from people who have had money drained from their accounts, sometimes without even getting the loan they were looking for.

In one of the most shocking cases seen by RBS, someone looking for a £100 loan ended up being charged £700 because their details were passed around 10 different middlemen.

It said that for every payday loan a customer takes out, they are usually charged two to three times by brokers, with these fees usually coming to around £70.

In July, brokers made more than one million attempts to remove money from its customers’ accounts, of which 25,000 attempts were successful.

The brokers tried to seize £60 million worth of fees collectively, but were able to acquire £1.1 million worth of fees. Transactions were usually unsuccessful because of a lack of funds in the customer’s account.

Terry Lawson, head of fraud and chargebacks at RBS and NatWest, said: ” We are actively working with the industry to raise awareness of these practices and in many cases halt some of the merchants’ operations.

“We are reaching out to customers to warn them of these fees and taking steps to block the transactions altogether, but, these are sophisticated organisations, they are resourceful and more needs to be done at an industry and regulator level to protect customers who may already be in vulnerable situations.”

RBS said that terms and conditions can be unclear on payday brokers’ websites and it can also be a struggle to find any contact numbers for them if there is a need to complain.

The Competition and Markets Authority (CMA) has been moving to clamp down on payday loan middlemen.

It recently proposed that such websites should be required to display messages such as “We are a broker, not a lender”, and “We sell your application details on the best terms for us rather than you”, before asking whether the customer still wants to go ahead.

The Financial Ombudsman Service (FOS), which resolves disputes between consumers and financial firms, said nearly 11,500 people have contacted it to complain about credit broking websites, which is almost double the number seen across the whole of the previous financial year.

Common themes it sees in complaints include consumers not recognising the business that took a fee, consumers not giving permission for the fee to be taken and people wrongly thinking that the payment had been taken towards the loan.

The service said that in the majority of cases, the businesses running the websites refunded the cash they had taken as soon as the ombudsman got involved.

In two-thirds of the complaints it went on to investigate, the ombudsman agreed that the consumer had been treated unfairly, while in the remainder of cases the fees had already been refunded.

In some of the worst cases the ombudsman has seen, consumers’ bank accounts were debited multiple times without warning, as their banking details were passed onto other credit broking websites.

Senior ombudsman Juliana Francis said: “It’s disappointing to see that more and more people are being misled into thinking that these credit broking websites will get them a loan.

“In too many of the cases we sort out, no loan is provided and people’s bank accounts have been charged a high fee, often multiple times.

“If money has been taken from your account unfairly or without warning, the good news is the ombudsman is here to help. Give us a call and we’ll help you quickly get things sorted.”A spokesman for the Consumer Finance Association (CFA), which represents short-term lenders such as the Money Shop and Quick Quid, but not brokers, said that if someone is unsure about a particular business or service, they should never disclose their personal bank details.

He said: “Brokers do not lend any money – they are simply the middlemen. There is no need to pay a fee to arrange a loan.”