One of the "big six" electricity and gas suppliers, Scottish Power came last in the ratings of 100 brands with 59% satisfaction only - and one stage worse than last year.

The survey of 3,500 consumers found the poorly rated firms to have "useless service and unhelpful standardised replies".

SP is not the only energy company to fare badly.

SSE had a top score of 74% while British Gas and EDF Energy had a success rate of 71% while npower just missed bottom slot with a satisfaction rating of only 61%.

Telecoms companies also irritated customers.

EE managed to garner 68% of the vote to come top of the telecoms poll, with Vodafone coming in at 66%, TalkTalk at 64% and BT at 63%.

The poor performance of the telecoms firms set a "worrying trend" for the industry, the watchdog warned.

No-frills airline Ryanair is still, despite its well-publicised efforts to improve customer service, in the bottom five of the unpopularity stakes coming in at number 95.

Customers explained their dislikes clearly, ranking the lowest for disloyalty, inflexibility and long waits, all of which made their customers feel like a nuisance.

Which? executive director Richard Lloyd said: "Long-suffering customers deserve better, as once again essential services that we all rely on have been caught falling down on how they treat people.

"Nearly nine in 10 told us poor service puts them off using a company again, so there is a clear incentive to offer service that makes customers smile.

"Companies at the bottom of our survey should take note: make your customers seethe and you will pay the price."

A Scottish Power spokesman said: "We would like to reassure customers that we are committed to restoring our service levels to the highest possible standards.