Households are facing the prospect of more energy price hikes after Scottish Gas owner Centrica warned its costs continued to mount.

The UK's biggest energy supplier, which has more than one million Scots customers, dropped its standard electricity tariff by 5% in January after big rises in both gas and electricity bills over the summer.

But it warned that the trend for retail energy costs "remains upwards", with wholesale gas prices 15% higher for next winter and other costs set to add £50 to the cost of supplying the average household this year.

A round of price reductions by the UK's major suppliers earlier this year were not enough to offset price hikes over previous months, and utility bills have been a major contributor to rising living costs, squeezing households.

British Gas, with 15.9 million residential customers, upped gas bills by 18% and electricity by 16% in August.

As well as the rise in wholesale gas prices, Centrica said it was battling with higher costs for transport and distribution, metering, green levies and social costs.

Centrica's warning came as it said its own trading this year was in line with expectations. Cold and wet weather boosted demand in April, leaving average domestic gas consumption in the first four months of the year 1% higher than a year ago, although electricity was down 3%.

Residential customer numbers were broadly unchanged from the start of the year, helped by January's tariff cut, which it said re-established it as the cheapest major electricity supplier in Britain.

Its business customers' average gas and electricity consumption was down by 1% and 4% respectively, and its profit margins were under pressure amid the recession.

Audrey Gallacher, director of energy at Consumer Focus, said: "Consumers will need clear evidence that price rises are warranted if they are to stomach further increases to their bills.

"People simply don't know whether what they are asked to pay is fair – the perception is that suppliers are quick to pass on high price rises and slow to pass on small price cuts.

"Much greater transparency on costs, pricing and profits is needed," she added.

She called for the extra revenue the Government receives from carbon taxes to be used to help people who are being hit hardest by rising costs.

Tom Pering, an energy analyst at Inenco, said cost hikes were caused by a combination of issues, including supply security and the increasing cost of Government legislation.

He added: "This increased cost will inevitably be passed on to residential and business customers in the form of higher bills. However, the big six energy companies are still not doing enough to inform UK households of their cheapest tariffs and helping them reduce bills."

Rutherglen and Hamilton West MP Tom Greatrex, Labour's Shadow Energy Minister, said: "Hard-pressed families and pensioners in Scotland struggling to make ends meet thanks to the recession made in Downing Street will be astonished that the owners of Scottish Gas, who made billions in profits and paid out millions in bonuses last year, are now threatening another round of price hikes.

"When wholesale prices rise, energy bills go up like a rocket. But when they fall, bills come down like a feather. Instead of letting the energy giants get away with trying to soften up their customers for bumper bills, the Government must make the energy companies come clean about the price at which they buy and sell energy."

Centrica's shares were up 1% after it said it was trading in line with expectations.

The City expects underlying operating profits to rise 20% to £2.9 billion in 2012. Its UK residential energy supply business is expected to see profits rise 13% to £592 million.