THE chief executive of the Royal Bank of Scotland has called on regulators to act over 'free product trial' scams - which cause consumer to lose typically £80 from their accounts.

Ross McEwan has spoken out after the bank's fraud department detected what he described as new type of scandal involving companies that claim to offer free trials of nutrition and beauty products but then take large payments from customers a few weeks later.

Trading Standards departments have been alerted to the 'free trial scams' in the run up to Christmas, concerned they encourage shoppers to sign up to receive a free trial of a product.

People are asked by the online tricksters to provide their credit or debit card details. They are then automatically subscribed to a membership costing on average between £70 and £90 a month.

The most popular products covered by the scams include anti-ageing products, teeth whitening kits, diet pills and nutritional supplements which are advertised on Facebook and website pop-ups.

There has been particular concern following an explosion of online ads for diet products boasting how you can 'lose weight and feel great' once you have signed up to receive a free trial bottle of pills.

The concerns surfaced as customers have complained to banks about payday loan brokers taking fees from their accounts unexpectedly.

Mr McEwan called on lenders to stop financing companies that extract unauthorised payments from customers' accounts.

In an interview with the Financial Times he said: "Stop taking from one hand and saying they are bad, yet .��.��. taking the fees out of them. There are very few, for example, payday lenders that we will ever deal with."

It is understood victims have faced difficulties in recovering subscription fees if they have agreed to the terms and conditions of the trial without reading them fully - as the charges are usually buried in the small print.

And trading standards officers have also warned consumers face further issues if companies are located outside the UK, as it makes it hard to hold them accountable.

The only way to stop the charges is by ordering the bank to halt them - after first cancelling the agreement with the provider.

Continuous payment authorities are different from traditional standing orders that must be set up between the customer and bank - not provider - and are for fixed regular amounts.

Mr McEwan said the issues were heightened when consumers were unable to work out how to stop the payments or contact those responsible. In some cases, customers were asked to confirm terms and conditions before they had appeared online.

"They are making it so difficult for people to actually stop the payment," he said. "We are going to work through who are the players, who are the worst at it and to start calling it out with the regulators."

The number of complaints received by Citizens Advice about slimming pills has risen eightfold in two years to more than 1,500 for the three months from April to June 2014.

The banks says it had around 400 calls a day last August from customers about unauthorised free trial payments but this had dropped to 50 calls per day.

Some £2.9m in total was taken in this way from 37,000 RBS customer accounts between June and January this year.

Terry Lawson, head of fraud and chargeback operations at RBS, said: "We've engaged with Visa, MasterCard, and the UK Cards Association to bring the matter to their attention. They have managed to clamp down, but we are monitoring that, to find out who the offenders are."

The bank said it was ensuring that no further transactions go through for customers who have complained, but the lender said it could not refund those who have been affected.