ENERGY giant Scottish Power has come under fire from a consumer watchdog after keeping customers on hold for 30 minutes.

The Iberdrola-owned firm was found to be the worst performing in the survey conducted by Which? looking at the call waiting times of 16 energy suppliers across the country, for both customer service and sales calls.

Callers to Scottish Power's customer services line were kept on hold for an average of 30 minutes, while those who called the sales team received an answer in 49 seconds.

Which? executive Richard Lloyd has branded the findings unacceptable and urged Big Six firms to do more for their customers.

Mr Lloyd said: "It's unacceptable that some energy suppliers expect their customers to wait on the phone for so long just to ask a question, give meter readings or complain. With average waiting times of up to half an hour, it is clear some suppliers need to do more for their customers.

"Our research shows only a quarter of us trust our gas and electricity supplier which is why we need major reforms to Fix the Big Six. Suppliers must act rapidly improve basic standards in customer service and not wait for the outcome of the competition inquiry."

The findings released today were gathered in October by mystery shoppers on behalf of the consumer watchdog.

Callers contacted the companies 12 times at set times of day, and recorded how long they had to wait for both sales and customer services enquiries.

The best-performing supplier, Ebico, answered its customer service calls in 30 seconds and sales calls within 47 seconds.

Those calling for a sales enquiry were kept waiting the longest by Spark with an average queuing time of more than 12 minutes.

NPower was found to have improved on its call answering times by around 17 minutes compared to last year, answering customer service calls on average in two minutes 26 seconds.

Glasgow-based Scottish Power was told last month by the regulator Ofgem it must shorten average call waiting times to two minutes by the end of January or face a sales ban.

The firm also agreed a £2.4m consumer redress package with the regulator last week following the a ruling that it failed to deliver energy efficiency measures on time.

The payments will be put towards charities and funds for vulnerable consumers.

A ScottishPower spokesman said: "In the last six weeks we have seen our average speed of answer reduce significantly to just over 2 minutes, and we are continuing to make improvements in this area. Sixty per cent of our calls recently have been answered in under 20 seconds.

"The transition to our new £200 million customer IT system has been challenging, and we apologise to any customers who have experienced difficulties contacting us. We are increasing our staff by a further 250 people on top of the additional 450 people already recruited earlier this year to manage all customer contact and complaints as quickly as possible.

"We also continue to have the longest call centre opening hours in the industry, and we are committed to restoring our customer service levels to the highest possible standards."