Customers who use a small amount of cheap energy in their home are likely to be hit hardest by ScottishPower's price hikes.
According to MoneySavingExpert, most energy tariffs are split into two tiers, with customers paying a higher rate for the first few units used, before the cost for each unit falls to the second tier rate.
However, the energy supplier's first tier rates are set to soar when the price hikes are implemented later this year, meaning householders who only use enough energy to stay on tier one rates, will see their bills soar.
The website calculates that tier one prices for a unit of electricity will go up by 29 per cent, while a unit of gas will cost 23 per cent more when prices go up in August.
Make sure you're not paying too much for your energy - compare gas and electricity prices now at energyhelpline.com or call 0800 074 0745