COMPLAINTS by bank customers have more than doubled in a year due to a surge in cases over the mis-selling of payment protection insurance (PPI) on loans and credit cards.

New data shows that Lloyds Banking Group, which includes the Bank of Scotland, was among those experiencing the biggest leap in complaints, receiving 860,000 in the first six months of this year, up 146% on a year ago. Representations about general insurance including PPI more than trebled to 738,000.

Royal Bank of Scotland received about 492,000 complaints for its RBS and NatWest brands, up 128% from a year before, with grievances about general insurance rising to 365,000 from 78,000 a year earlier.

Millions of customers of the group, which is majority owned by the UK government, were unable to pay bills, view their transactions online or receive payments, including wages, following an IT meltdown in June.

A spokesman for RBS said: "Our IT outage on June 19 created great inconvenience for our customers and additional pressure to resolve complaints. We are determined to win back our customers' trust. Since then we have resolved 99% of 44,215 incident-related concerns."

Barclays yesterday insisted that its rise in disgruntled customers over the first six months of the year was "a small blip" on an improving trend. Figures showed there were 442,266 complaints opened in the first half, a 76% rise on the first six months of last year.

PPI complaints jumped by 280% compared with the same period last year, with 280,358 complaint cases opened. But if PPI is stripped out, the number of complaints would have fallen by 9% on a year ago, according to the bank.

Paul Maddox, managing director of customer service at Barclays, said bogus complaints brought by claims management companies (CMCs) "significantly distorted" the figures. More than one-third of CMC complaints were shown to be "vexatious", which slowed the speed at which Barclays could deal with genuine claims, he said.

"Setting these aside, we are on the right track in addressing the root cause of complaints," Mr Maddox said.

Customers have become increasingly aware of the availability of compensation for mis-sold payment protection insurance – where lenders sold worthless policies to cover loans and credit cards payments if they fell ill or became unemployed.

But many of them did not want or need the insurance.

Consumers have been encouraged by no-win no-fee claims management companies.

The PPI scandal has now resulted in provisions of more than £10bn from UK banks.

Antony Jenkins, Barclays Group's new chief executive who has the job of restoring the bank's tarnished reputation following a series of scandals, said the number of complaints was just 2% higher than in the second half of last year.

"Barclays has made significant advances in putting the customer at the heart of our business and we continue to break new ground, launching new technologies and remaining extremely competitive across our entire product range, which is attracting more customers," he added.

HSBC UK received 170,000 complaints, up 73% from a year ago, after PPI cases more than quadrupled to 102,000.

Santander UK received 241,000 complaints, up 42% on a year ago.