SCOTTISH Power has been named as having one of the three 'most dreaded' call centres in the UK.

The energy giant, together with BT and Talk Talk, ranked bottom of a 7000 customer survey satisfaction survey based on staff knowledge, phone menu system, politeness, helpfulness and waiting times, Which said.

They all scored an overall rating of just one star.

A Scottish Power spokesman said: "We had a very challenging period following the introduction of a new £200 million customer IT system, and we apologise to any customers who experienced issues.

"Major improvements have been made recently and our call response times have improved significantly since this survey was undertaken. In April 2015, customer calls were answered in 60 seconds on average and this is one of the best levels in the industry. Our call centre opening hours are also the longest in the industry."

Meanwhile, a Scottish Power advert for a remote control heating system has been banned over claims it could save customers up to 20% off their gas bills.

The advert on the provider's website claimed a trial of the Connect Remote Heating Control in 70 homes found they were using their heating 20% less of the time compared with others.

Scottish Power Energy Retail said a survey by a third party found 60% of the trial participants who engaged remotely with the product more than once a week had their boilers on for an average of 21% less than those who used it less than once a week.

The "Big Six" energy firm said it had amended the headline claim to make it clear that the data showed that a user could reduce their gas heating usage by up to 20% by using the product, and that the claim was based on a sample of 70 homes.

The Advertising Standards Authority (ASA) said consumers would understand that if they bought and used the product, which allows them to adjust their heating and hot water remotely, they could save up to 20% off their gas heating bills.

They said: "We considered that the trial did not demonstrate that there was a causal relationship between a customer's engagement with the product and their energy usage.

"For those reasons, we considered that the evidence provided was not sufficient to substantiate the claim that the product could result in a reduction in energy usage or a corresponding reduction in a user's gas bill, and concluded that the claim was misleading."

The ASA said its own review of the trial data was "problematic" because it found the survey did not adequately control for other factors that could influence energy usage, such as the number of people living in a home or the size, age and design of the house.

It ruled the advertisement must not appear again in its current form and told Scottish Power "to ensure they held sufficient evidence" to substantiate any claims.