SNP chiefs have apologised after European election mail shots were sent out incorrectly addressed – with Scottish Liberal Democrat leader Willie Rennie apparently receiving one addressed to "Edna".

Nicola Sturgeon's party said "some" of the 400,000 letters sent had the wrong name on them as a result of a "clerical error".

The party has now referred itself to the UK Information Commissioner’s Office (ICO) to see if there was a data breach.

Senior party figures blamed SNP HQ, which is run by Nicola Sturgeon’s husband Peter Murrell, for a mistake in the data given to mailing company Critiqom.

Murrell’s name appears on every letter as its official promoter.

Asked in 2016 if she would ever fire her husband as party chief executive, Ms Sturgeon told the Sunday Herald: "If I thought it was merited."

Rennie posted a picture of a letter addressed to "Edna Rennie" on Twitter.

He said: "I will insist that @NicolaSturgeon addresses me as Edna in the @ScotParl."

But with reports claiming thousands of letters had been sent out with incorrect details, Labour and the Conservatives raised concerns of a possible data breach.

The Tories said one woman in the Berwickshire, Roxburgh and Selkirk constituency had received 30 letters to her home – but that not one of them had the right name on.

Scottish Labour health spokeswoman Monica Lennon also posted a picture of the letter, asking: "Who is George Mackie and why does @NicolaSturgeon think he lives in my house?"

An SNP party insider told The National's sister paper, The Herald, that there appeared to have been “spreadsheet” problems, with small errors rippling across thousands of names and addresses.

The source said younger voters would probably brush off the problem, but the party was worried that older voters – those most likely to vote – would be annoyed.

“The problem is losing that personal touch older voters like,” the person said.

Scottish Conservative MSP Murdo Fraser said: "The SNP has become so incompetent it can't even carry out a simple mailing exercise."

He added: "This wasn't just inconvenient and confusing for tens of thousands of householders.

"It's a very serious data breach, and one that could land the party in all kinds of trouble.

"The SNP should apologise immediately, and refer itself to the Information Commissioner."

LibDem MSP Alex-Cole Hamilton also said it is a data breach, saying: "Is this not a MASSIVE GDPR violation? Hearing that it’s country wide as well..."

Labour MSP Neil Findlay said: "This is an embarrassing blunder from the SNP.

"No wonder our public services are in such a mess when they can't even post a letter properly.

"This incident may have resulted in individuals' personal data being passed on to strangers.

"The SNP should apologise to all those affected by this blunder."

An SNP spokesman said: "On Thursday mail arrived with some electors that had the wrong addressee name on the letter.

"A clerical error has been identified in our office. We have been in touch with the ICO, but there is no ongoing issue with the integrity and security of data or any issue of identity theft.

"We wish to apologise to the electors affected."