THE SNP leadership has called on Theresa May to apologise for her “cynical attempt to smear” the party in what it said was a bid to distract attention from the Conservatives’ own election expenses scandal.

During her response to the decision by the Crown Prosecution Service not to pursue criminal charges against up to 20 Conservative candidates for alleged election expenses fraud during the 2015 campaign, the Prime Minister said: “If you look at the expenses issue, we have seen all the major parties and the Scottish Nationalists being fined for mistakes made on national expenses. We have paid our fines and I sincerely hope the other parties are paying theirs."

In March, the Tories were fined a record £70,000 by the Electoral Commission for "numerous failures" in reporting its expenses for the 2015 election and three by-elections in 2014.

However, the Nationalists insisted Mrs May’s claim about the SNP was wrong and that the party had never been fined for breaching election expenses rules.

Nicola Sturgeon took to Twitter saying: “PM should apologise for this attempt to smear @theSNP - unlike Tories, we abide by rules and have never been fined by Electoral Commission.”

Noting how Tory HQ had declined to respond to press enquiries seeking a response, Pete Wishart, the SNP candidate for Perth and North Perthshire, said: “Tory HQ has gone into lockdown, refusing to answer straightforward questions from journalists about the Prime Minister’s cynical attempt to smear the SNP.

“The reality is that unlike the Tories, who were hit with a record fine, the SNP has always stuck to election rules and never been fined.”

He added: “Theresa May was wrong and she knows it. But the deafening silence from her party speaks volumes. Unless she apologises, people shouldn't take a single word she says in this election at face value.”

The police had launched investigations into at least 30 individuals, including Tory candidates, centring on allegations highlighted by Channel 4 News and the Daily Mirror that expenses relating to busloads of Conservative activists sent to key seats were reported as part of national spending rather than falling within the lower constituency limits.

In announcing its decision, the prosecuting authority explained that, even though spending returns submitted by some of the Tory candidates and officials might have been inaccurate, there was insufficient evidence to prove they were knowingly dishonest.

Mrs May stressed that the prosecutors' decision had confirmed Conservative expense returns were "properly reported and properly declared" and the party's election candidates under investigation had done nothing wrong.

Her colleague, Sir Patrick McLoughlin, the Conservative Party Chairman, claimed the allegations were “politically motivated”.

But the First Minister insisted the Tories still had "significant questions to answer" over their election expenses and called for a review of the Commission's "clout".