This is Scottish Power’s second price rise this year, with dual fuel prices rising by 5.5% on 1 June. It follows Ofgem’s decision to increase the level of their Safeguard tariff.

The company said the rise was due to wholesale energy costs having risen by more than 20% since April.

The UK government said it was “disappointing that Scottish Power has announced another price rise in its default tariff at a time customers are already paying more than they need to”.

A spokeswoman for the Department for Business, Energy and Industrial Strategy said: “This is why the government is introducing a new price cap by this winter to guarantee that consumers are protected from poor value tariffs and further bring down the £1.4bn a year that customers have been overpaying.”

Citizens Advice Scotland energy policy officer, Craig Salter, said: “Today we’re seeing another price hike that will hit the least well off the hardest. This is Scottish Power’s second increase this year, and for those who are struggling it will make it even harder to make ends meet.

“If we are to see ongoing price increases across the board that are unaffordable for households, there is a clear problem with affordability in the energy market that needs to be addressed. With over a quarter of Scottish households still in fuel poverty, it is unacceptable that consumers continue to be failed by the market in this way.”