John Swinney has insisted Parliamentary stamps have not been used for the SNP's “election purposes.”

Speaking to the BBC’s Laura Kuenssberg, the First Minister said he was “confident” no public money had been used to fund his party's campaigning.

Last week, the Scottish Parliamentary Corporate Body launched an investigation after a whistleblower claimed postage paid for by the taxpayer was being used by SNP candidates to contact voters.

READ MORE: Whistleblower accuses SNP of misusing public funds for election

The complaint, made to Alison Johnstone, Holyrood’s Presiding Officer, included screenshots of a WhatsApp group, called “Office Manager Chat” with senior staff members asking if the stamps can be traced.

More conversations emerged on Sunday morning, including a comment from someone who works for Mr Swinney.

One staff member said: “Embarrassed to say I inherited a lot — and I mean a lot — of 2nd class stamps”.

An individual in the First Minister’s office replies: “The stamp fairy is very useful when it comes to campaigns!”

The original poster then says: “I know, even that won’t make a dent in them! I’ll whisper the amount I have next time we meet.”

Asked about the comments, Mr Swinney said: “Well, I've obviously discussed this with my staff, and I've been assured that no parliamentary stamps that have been provided by parliament have been used to support election purposes.

“And obviously, the parliament has said that they're looking into this matter, and obviously we'll provide parliament with any assistance that they require as they undertake those inquiries.”

Asked who the stamp fairy is, the First Minister said: “Well, we campaign on a regular basis in my capacity as a member of parliament, so we're engaging with the public on a countless range of different issues.

“So I think these are sort of humorous remarks made in a WhatsApp channel. And what's important is the reassurance that I've had, that parliamentary stamps have not been used for election purposes.”

Asked if he was completely sure that his party had not been using any public money to fund his election campaign, Mr Swinney replied: “I'm confident of that.”

He added: “We've obviously been engaging in a fundraising campaign to support the election campaign.

“It's been supported by the many members that we have around about the country.

“The Scottish National Party is fortunate that we have the largest membership of any political party in Scotland.

“Indeed, we've got more members than all the other parties combined and those members have been supporting our election campaign and enabling us to have the resources available to us generated and raised from within our party membership base to support us in our campaigning activity.”

Speaking to LBC later on Sunday, the First Minister agreed it would be “completely unacceptable” for resources to be used in this way.

“The rules are clear that parliamentary stamps that are procured for that purpose should be used for parliamentary activities,” he said.

He added it is “important” for those in question to co-operate fully with parliamentary authorities.

MSPs are allowed to spend up to £5,500 a year on postage and stationery.

The parliament’s rules state that they “must be used only for parliamentary duties and must not be used for any other purpose, including party political purposes”.

In the screenshot of the WhatsApp group attached to the initial complaint, one individual, who is named as “Paul” in the conversation, posted a message that read: “Guys, the new stamps. Can they be traced?”

A staff member who works in the office of Nicola Sturgeon asked if he was referring to “who purchased them and what they’re being used for.”

Paul responded: “Can they be traced back to who purchased them?”

A member of SNP deputy leader Keith Brown’s office said she had “asked [a non-SNP staff member] in the mailroom and he said no”.

Another staff member said they were not aware of the stamps being traceable.

Someone from the office of Shirley-Anne Somerville replied: “If they can then a few people may be up in front of corporate body…”

In the email to Ms Johnstone, the individual who made the complaint said: “I am anonymously sharing a screenshot from the SNP office managers’ WhatsApp group chat due to my concerns that several MSPs are using stamps paid for by Scottish parliament expenses to pass to UK parliament election candidates for campaign activities such as sending target letters to hard-to-reach addresses.

"I’m concerned about this open discussion involving several members’ offices.”

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Dame Jackie Baillie, Scottish Labour’s deputy leader, said: “These are deeply concerning allegations and they must investigated fully. The SNP has a long record of failing to treat public money with respect and uphold the standards of transparency we all expect.” The Scottish Conservatives said: “The rules are clear. It’s for the SNP to answer if they have stuck to them.”

The Scottish parliament said: “We take the use of publicly funded resources very seriously. Officials are investigating the matter to establish whether there has been any misuse of parliamentary resources.”

The SNP has struggled for cash in recent months. That is likely, in part, down to Operation Branchform, the police investigation into the party’s finances.

Most of the income received by the party this year has come from Short Money, public cash given to all opposition parties in the Commons with two or more MPs.