ENERGY giant Scottish Power has haemorrhaged 120,000 customers, its latest results reveal.

The loss of customers switching to cheaper deals elsewhere has cost the "Big Six" firm in retail supply earnings, with a fall of more than 60 per cent recorded.

Three quarters of the customers have left the supplier since the end of June alone, taking numbers from 5.34 million last year to 5.22m at the end of the third quarter.

Retail supply earnings have fallen to £59.4m from £152.3m as a result.

However, ScottishPower boss Keith Anderson says the Spanish-owned firm is outperforming its rivals, stating: "In Retail, we have more customers on fairer deals than any other Big Six suppliers and we are the only bigger company to have increased its market share since 2011.

"We believe that putting our existing customers before new customer is the best way to compete in this marketplace. That is why we work hard to reward our customers’ loyalty by getting them onto better deals."

Commenting on the results, Anderson also criticised UK Government plans for a price cap on standard variable tariffs. An "absolute cap" will be imposed as a temporary measure on poor-value deals, lifting by 2023 at the latest.

ScottishPower has pledged to end standard variable tariffs and move customers on to cheaper fixed deals, as have several of its rivals.

Anderson stated: "Our view remains that the proposed price cap will not help to engage those customers who could still find a better deal.

"It will be bad for consumers, energy companies big and small, as well as investor confidence.

"The key question the government needs to answer is whether they still believe customers benefit most from free market competition. If they do, any intervention must be designed to increase consumer engagement, which is the biggest thing wrong in this sector. Otherwise, we would urge the government to opt for a fully regulated market. We need clarity one way or the other.”

The company's earnings have also been dented by recent mild weather, with demand for both gas and electricity dropping by almost seven per cent.

Its UK generation business also had a tough three months, reporting a loss of £12.9m against earnings of £34.8m a year earlier.

Overall, earnings fell by 75 per cent to £46.5m for the UK generation and supply arm.

However, ScottishPower did achieve improved results in its renewables division. Earnings went up by more than one third to £211.6m as wind production increased.

The company reported a near-40 per cent uplift in onshore wind alone during the third quarter, compared with the same period in 2016.

The firm also passed two significant milestones during the third quarter of 2017, reaching two gigawatts of renewable energy capacity in the UK and completing a £650m two-year programme of construction for eight new onshore wind facilities in Scotland.

Anderson said: "ScottishPower continues to invest heavily to deliver a clean, reliable and fairer electricity system for the UK despite continued political uncertainty."

The wider Iberdrola group achieved an 18 per cent rise in net profit to £2.1 billion as a better international performance offset poor results in Spain. Brazilian subsidiary Neoenergia, which is 52 per cent owned by Iberdrola, was named as a "key growth driver".