MANY leading banks, insurers and energy companies are making existing customers pay to phone them while offering free numbers to new customers, a watchdog has found.

Some 27 out of the 34 companies offered 0800 numbers for new customers, while just six gave the free numbers to existing customers, Which? said.

The companies reportedly operating a two-tier system by making existing customers use an 0844 or 0845 number included ScottishPower, Churchill, HSBC and NatWest/RBS.

Twenty companies made customers call the often-expensive 0845 numbers to complain.

Which? said customers were faced with a "baffling" number of different charges.

The watchdog wants greater transparency.

Which? executive director Richard Lloyd said: "It is unbelievable that companies would add insult to injury by charging their customers a premium to make a complaint."

A ScottishPower spokesman said: "As part of our commitment to clear price comparisons, we have always had a free phone number for customers to discuss tariffs. For our main customer service lines, we operate 0845 numbers. ScottishPower also offers a call back service."