The Scottish National Party has warned that the government's energy plans could see the cost of generating electricity north of the border soaring.

Attacking the Energy Bill on Monday, the nationalists said that its effect would be to subsidise power generators in the south of England at the expense of those in Scotland.

The SNP is concerned at measures to create a single electricity market across Great Britain.

At a press conference in Aberdeen, the party expressed concerns at Ofgem's planned "zonal pricing" which, it warned, could see National Grid Company charges in the Scottish generation area rise from £5.44 to as much as £20.69 per kW while charges in central Scotland could rise from £2.45 to £11.28.

In contrast, said the SNP, companies which build a new station in central or southwest London would gain a subsidy of £7.05 per kW.

Such cost increases would jeopardise the economics of key Scottish power stations such as Longannet and Peterhead, ministers were warned.

And attempts to increase the proportion of power generated from renewable sources could also be undermined.

The SNP said that while the government had offered amendments which would protect renewables for up to 10 years, this timescale is too short to make any difference over the lifetime of large projects.

"The current proposals could turn into a disaster for Scottish generators and consumers and hole the drive for renewables below the waterline," said Alex Salmond, the party's Westminster leader.

"This mumbo jumbo from Ofgem is nothing more than a cover for a subsidy for the south while Scottish generators are asked to pay through the nose for the privilege of producing electricity."

And nationalist MP Mike Weir said ministers were "insane to even give this nonsense the time of day".