New figures from the Electoral Commission show the party spent £99,000 on the Holyrood by-election in August, compared to £90,000 on the referendum on leaving the European Union in 2016.

The SNP's Shetland candidate came second to Lib Dem Beatrice Wishart in the poll.

The Scottish Liberal Democrats have hit out at the SNP over the election spending figures, which show the party spent 12.8% of the total allowed on the Brexit poll.

"The fact that the SNP spent more on the by-election in Shetland than in the entire EU referendum campaign speaks volumes," critics say. Picture: PA

Orkney and Shetland MP Alistair Carmichael claimed the party's spending on the EU referendum is evidence of the "cynicism of the SNP leadership's position on the EU".

Brexit: EU and UK still have 'significant issues to resolve'

He said: "The fact that the SNP spent more on the by-election in Shetland than in the entire EU referendum campaign speaks volumes. It is disappointing but hardly surprising, considering how much lucre they flashed around in the Northern Isles over the summer.

"Apparently one more vote for independence in Holyrood was worth more to the nationalists than their European values. It's a shame they don't put their money where their mouth is.

"It shows the cynicism of the SNP leadership's position on the EU. They tell their supporters one story on Europe, but their actions tell another.

"They back the EU with words, but the truth is that they see Brexit as a golden opportunity to push independence at the price of our country's well-being."

The Shetland by-election, which was called after the resignation of Tavish Scott, saw Ms Wishart take the seat with almost 48% of the vote.

The First Minister, along with a number of other high-profile SNP members, made several visits to Shetland ahead of polling day.

SNP spent more on Shetland by-election than Brexit vote