The energy giant sought to calm nerves last night after a Madrid newspaper claimed its Spanish-based parent company Iberdrola might face a break-up if Scots vote Yes in the referendum.
Business daily Expansión claimed independence threatened a special EU opt-out that exempts ScottishPower from European competition rules banning firms from both generating and transmitting electricity.
Under the headline "London warns Iberdrola of its high risk in Scotland", the paper said the Spanish giant could be forced to sell its transmission network in the north of Great Britain.
ScottishPower, in its first statement on the independence debate, dismissed any suggestion it faced a break-up.
A spokesman said: "This is not an issue. It has not been raised with ScottishPower at any level."
The Expansión story came after the UK Government boasted of its role in securing the opt-out for both ScottishPower and its rival Scottish and Southern Energy in an analysis paper on EU issues unveiled by Foreign Secretary William Hague in Glasgow earlier this month.
Expansión reported: "In the opinion of Unionist parties, this exception could be at risk because of the independence process launched by the Scottish Government led by nationalist Alex Salmond."
This assertion was not sourced.
A Whitehall source last night said he was not aware of anyone in the Government making any approach to Iberdrola. However, stressing the UK view that Scotland would have to reapply for EU membership from scratch, he said: "There are a number of areas where the UK enjoys favourable positions which are cast in to doubt and uncertainty for the new applicant."
He added: "Some opt-outs may be easier to negotiate than others."
ScottishPower and SSE are "vertically integrated" companies, meaning they have both generation and transmission wings. EU regulators prefer the two types of business to be split, as in England, where the national grid is run by one company and power stations by others.
A Scottish energy industry source said he did not believe there would be any difficulty renewing the opt-out if Scotland were to become independent.
Ireland, he explained, has a similar "derogation". He said: "This is a European rule that would be applicable to the Scottish vertically integrated energy companies whatever the outcome of the referendum."
Expansión described any break-up of ScottishPower as a "grave setback" for Iberdrola. The assertion raised eyebrows among independent brokers. JB Capital Markets in a bulletin said it would expect Scotland to justify the original opt-out.
Downing Street previously denied Spanish reports it has formed an "anti-separatist" pact with the Conservative Government of Mariano Rajoy, who faces an unsanctioned independence referendum this year in Catalonia.
The Herald's sister paper the Sunday Herald this week revealed diplomatic cables showing the UK Government distributing papers critical of independence to its embassies to be forwarded to "host governments and other local contacts".
SNP MSP James Dornan blamed Whitehall for the Iberdrola story. He said: "Not content with spreading ever more ridiculous scare stories in Scotland, the UK Government now appears to be coming up with ludicrous threats to our neighbours across Europe. One only wonders how widespread this scaremongering has become."