SCOTTISHPower has come under fire for an "unjustified" £63 rise in energy bills for almost one million customers.

The Glasgow-based company has become the third of the 'big six' energy providers to hike prices this month.

ScottishPower, which is owned by the Spanish energy giant Iberdrola, blamed the 5.5 per cent increase on rising wholesale energy costs, delivering greener electricity and upgrading meters.

The Herald:

But Claire Perry, energy minister, said the price hike was “unjustified” and “extremely disappointing”.

She added: "Consumers should vote with their feet - changing suppliers can help consumers get the best deal, saving around £300 by ditching a default tariff offered by the Big Six.”

READ MORE: Scottish Power profits tumble as energy giant loses 120,000 customers

She has already condemned Scottish Gas for an identical percentage rise announced earlier this month.

Perth-based SSE and npower are the only two other big energy firms yet to declare a price rise, before the government’s planned cap on standard tariffs later this year.

The ScottishPower rise takes effect on June 1 and will affect around one in three customers. It comes a year after it raised prices by 7.8 per cent.

The Herald:

Neil Clitheroe, chief executive of retail at ScottishPower, said: “Unfortunately our standard variable prices are increasing. This reflects rising wholesale energy costs and compulsory non-energy costs. Two-thirds of our customers are unaffected.

“We will be contacting all customers affected by the price change to give them the opportunity to move to a fixed-price-tariff alternative and avoid this increase.”

READ MORE: Scottish Power rated amongst worst power suppliers in UK for complaints

Brian Sloan, Age Scotland’s chief executive said the price hike was "very disappointing" and said ScottishPower and other energy companies "need to do more" to help their most vulnerable customers and work with the Scottish Government to end fuel poverty.

The Herald:

"Older people are likely to be hardest hit by this rise, with more than half of single pensioner households and four in ten pensioner couples already living in fuel poverty," he said.

“We hear from older people around the country who are struggling to pay their fuel bills, often cutting back on other essentials such as food. People with health conditions are most affected, with many putting their health at risk by not heating their homes adequately."

Ofgem, the energy regulator, said: "Any price rise for consumers is unwelcome, particularly for those who are already on poor value tariffs. Ofgem is working with the government to protect all consumers on poor value default tariffs from being overcharged by suppliers by introducing a default tariff price cap."

READ MORE: Scots energy firms 'amongst bad boys of shocking waiting times'

The Department for Business, Energy and Industrial Strategy said the price rise makes Scottish Power’s default tariff the most expensive of all the Big Six.

MoneySavingExpert.com founder Martin Lewis said: "Here we go again, another energy company bleating like a sheep. British Gas set the lead and now, knowing they won't get smacked with the same level of publicity whether or not it's justified, we see the rest following along.

The Herald:

"But yet again, what ScottishPower customers and indeed customers of all big six energy companies need to know is that they are ripping themselves off by staying on a standard tariff."

Claire Osborne, energy expert with the price comparison site uSwitch.com said the rise will cost customers at least £60 million this year alone.

"Energy companies are now falling over each other to raise the price of their worst value deals," she said. "It's a fact of life that gas and electricity costs rise as well as fall, but larger suppliers who buy several years ahead should be able to factor in wholesale price fluctuations and protect their customers from sudden price rises.

"The threat of an impending price cap seems to be having a negative impact before it's even been introduced. Suppliers are rushing to push up prices for millions of customers and banking on them not switching once the cap is in place."

Which?, the consumer organisation said the hike was "a kick in the teeth for hard-pressed energy customers".

Ofgem recently raised a price cap on 5m vulnerable households and before the government’s wider price cap for 11m households on standard variable tariffs. That ceiling is due to take effect before the end of the year.

READ MORE: Scottish Power to cut 200 jobs after 'efficiency schemes'

Earlier this month the French state-owned supplier EDF Energy announced a smaller 1.4 percent increase for more than 1 million customers. E.ON was the first of the major energy firms to raise prices this year, announcing in March that about 1m households would face higher gas and electricity bills from April 19. The average annual increase was £22 but one in four households on the firm’s standard variable tariffwill have to pay an extra £50 a year.

For those on monthly direct debit with ScottishPower, average dual fuel bills will rise by £63 to £1,211 a year based on typical use - a 5.6 percent increase.

For those who pay by quarterly credit, average dual fuel bills will increase by £85 to £1,311 a year, based on typical use - a 6.9 per cent increase.

These estimates are based on typical annual consumption of 3,100kWh electricity and 12,000kWh gas.