The SNP has apologised after a costly clerical blunder saw thousands of voters sent letters with the wrong names attached.

Party mailings have been dispatched to the addresses of around 400,000 postal voters across Scotland ahead of the European election, including those which were correctly named.

However, there have been widespread reports across the country of wrongly-named letters.

The Scottish Conservatives estimated "tens of thousands of householders" were affected and urged the SNP to refer itself to the Information Commissioner (ICO).

The SNP said an administrative error had been identified in its office but insisted there was "no ongoing issue with the integrity and security of data".

The Royal Mail has declined to comment, but one local postal worker told STV News on Thursday: "The SNP have sent out EU election letters today.

"Almost every single one is the wrong name for that address in the whole office - maybe even every letter.

"But we have to deliver as addressed, even though all the posties know they are the wrong name.

"I had many of my customers handing the letters back."

Scottish Liberal Democrat leader Willie Rennie, who launched his party campaign's for the election on Thursday along with the SNP, poked fun at Nicola Sturgeon over the mistake.

He received a letter to his home address from the party addressed to "Edna Rennie".

One woman in the Scottish Borders reportedly received 30 such mailings to her residence - none of which were addressed to her.

The letter opens with the words: "With the Westminster parties making such a mess of Brexit, the European elections are Scotland's chance to make our voice heard."

It ends with the First Minister's printed signature.

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."

The Scottish Tories said the matter could give the SNP "all kinds of trouble".

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

"No wonder people are losing their faith that the hapless nationalists can govern a country.

"No sooner has Nicola Sturgeon declared a climate emergency than she ensures hundreds of trees die in vain.

"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."

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

An ICO spokesperson said: "We have been made aware by the Scottish National Party of an incident relating to election materials and will be making enquiries."

The European election will be held on May 23, with eight parties and two independent candidates competing in Scotland.