HOUSEHOLDERS face price rises of up to 15% for gas and electricity, with Npower preparing to lead the way with an increase in double figures today.

Npower has 90,000 customers in Scotland out of its four million UK-wide.

And other energy companies are also expected to raise prices.

Tim Wolfenden, head of home services at price comparison website uSwitch.com, said: "Price rises have been on the horizon for some time."

He warned Npower's decision to increase standard rates by 10-15% would "give competitors the green light" to follow suit.

Npower, owned by German company RWE, has already increased its online tariff for new customers, upping bills by 17% the week before Christmas.

But the latest move, accompanying the winter's first serious snowfalls in lowland areas, marks the first by an energy supplier to increase standard rates after last spring's price cuts.

A drop in wholesale energy prices in 2006 and early 2007 enabled suppliers to cut bills, with British Gas becoming the first major UK energy firm to announce decreases.

Npower dropped its prices at the end of April 2007 and, before today's expected price increases, has been the fourth-cheapest of the six biggest UK energy suppliers, according to uSwitch.com.

Its average standard dual fuel bill stands at £908 a year, the website said.

But today's announced increases could see the group become the second most expensive provider, behind Scottish Power, which charges on average £958 a year for standard dual fuel bills.

Its cuts in April last year saw the group trim prices by 16% for gas and on average by 3% for electricity.

Energywatch, the gas and electricity consumer watchdog, condemned Npower's news.

Spokesman Karl Brookes said: Consumers are always being softened up with talk of unavoidable' price rises.

"The wholesale price for gas has risen but all suppliers can decide to absorb more of that themselves rather than pass all the risk on to consumers."