There is no threat to the security of Scotland's electricity supply, according to the UK Government's Business Secretary Vince Cable.

Mr Cable said the possible premature closure of the coal-fired power station at Longannet in Fife would not impact on security of supply north of the border because energy can be imported from England.

His comments came after First Minister Nicola Sturgeon wrote to Prime Minister David Cameron urging the UK Government to carry out an analysis of electricity capacity margins in Scotland.

Her letter followed concerns raised by industry experts at a meeting of the Scottish Energy Advisory Board.

Scottish generators, including Longannet, account for around 12% of the capacity connected to Britain's high-voltage electricity network - but pay around 35% of the charges, according to the Scottish Government.

Last year it emerged that Longannet may be forced to close earlier than planned due to what the operator ScottishPower described as ''disproportionately high'' transmission charges to connect to the main grid network.

Ms Sturgeon said: ''The Scottish Government cannot accept a situation where levels of energy security in Scotland are compromised by energy policy and network operation decisions taken outside Scotland."

Speaking on BBC Radio Scotland, Mr Cable said: "This isn't an England versus Scotland issue."

He added: "Clearly there is an issue about the pricing and the connection into the grid, but that is determined by the regulator Ofgem, it is not determined politically.

"There is no issue about security of supply. I don't quite understand why this issue has flared up.

"For many years Scotland has exported energy to England on the national grid and that was a perfectly sensible arrangement.

"There is now the possibility that there will be a reverse flow for some years until the big renewable sources in Scotland come into play. That is not a problem. It is a secure national grid - there isn't a threat to security of supply."

On the closure of Longannet, he said: "We are talking here about the future of 2,000 people in the immediate area, these closures have got to be very carefully managed and in a sensitive way."

Scotland's Energy Minister Fergus Ewing told BBC Radio Scotland that Longannet is necessary to "meet demand".

He said the national grid's "assumptions about security of supply seem to be extremely optimistic".

"I think there are two issues here - security of supply in Scotland and the UK, and the immediate threat to Longannet and to the jobs there.

"I think it is a bit rich of the UK Government to say it has nothing to do with them, because surely as the Government they have ultimate responsibility for delivering security of supply.

"I think it is essential that we consider the very real issues involved here, which many experts in the power generation side of the industry believe mean that security of supply in the UK is far from guaranteed."