THE SNP scraped just below the legal spending limit in the Shetland by-election by deducting accommodation costs for days campaigners were not physically staying in rented properties.

The party’s declared spending in the bitter Holyrood contest was £1,042 below the £100,000 maximum allowed by law.

The Herald on Sunday can reveal that the SNP declared just £4,590 out of the £8,034 spent renting out two properties during the election, claiming the rooms were only used 57 per cent of the time.

One of the landlords used by the SNP told this newspaper that people paid rent on a property “whether they sleep in it or not”, however the party cited an occupancy on a “rooms used basis” in its spending returns.

If the full accommodation costs had been included, the party would have gone £2400 over the spending limit.

Opposition politicians have called for a probe into the spending, however the SNP said it had an "exemplary record" and dismissed the calls as 'idiotic' and 'frankly laughable'.

Electoral Commission guidance also says the “full commercial value” of party spending on behalf of a candidate should be declared.

It can also be revealed that the sole paperwork filed in the official spending return for almost half the SNP’s spending was a two-page note signed by Nicola Sturgeon’s husband.

The Scottish Tories demanded “complete transparency” from the SNP and urged the Electoral Commission to examine any discrepancies.

Triggered by the resignation of former Scottish LibDem leader Tavish Scott, the August by election was one of the hardest fought in years.

The SNP spent more fighting it that it did on the EU referendum in 2016, declaring it put £98,958 behind its failed bid to get candidate Tom Wills elected.

The campaign included three visits by the First Minister and a stream of appearances by SNP ministers, MPs and MSPs.

However the LibDems held on after spending £64,534 on candidate Beatrice Wishart.

The Herald has obtained the complete spending returns signed and filed by both candidates.

They show that, despite spending more than half as much again as the LibDems, the SNP return had just 56 pages of receipts compared to 196 pages of receipts from the LibDems.

Almost half the SNP’s spending was covered by a two-page note from Ms Sturgeon’s husband, the SNP chief executive Peter Murrell.

Written on October 7 to Mr Wills’s election agent Robbie McGregor, it listed 18 items to be filed as “notional expenditure”, meaning spending by the party on behalf of Mr Wills, that were to be included in the candidate return.

Totalling £46,533, these included £13,849 for ferry travel, £6980 for flights, £4226 in care hire, and £5741 on flats, hotels and guest houses on the islands.

The party also said it supplied £13,820 of staff costs.

However only one of the 18 items, for £232, was supported by a receipt from a supplier.

In contrast, the LibDems filed full receipts for their accommodation, flights, ferries and car hires, despite using many of the same suppliers as the SNP.

Despite their bigger campaign, the SNP’s reported staff costs were much smaller than those of the LibDems, who said a third of their money, £22,856, was on agent and staff costs.

Critically, the SNP costs involved discounting almost half the cost of renting short term lets in Shetland for the 42-day campaign.

In one instance, the SNP rented a house for visiting activists with four double-bedrooms at Upper Hillside in Gulberwick from Shetland Property Lets for the equivalent of £81.29 a night.

The bill for the duration of the 42-day campaign was therefore £3414.18.

However Mr Wills only declared £1950.96 on his spending return after citing a “rooms used” basis equivalent to 57%, as if the property had been empty and cost-free for 18 of the 42 days.

This trimmed £1463.22 off the declared spending, more than enough to make the difference between staying under the spending limit and breaking it.

Shetland Property Lets said it rented properties to people based on a tenancy arrangement and did not reduce its bill if not all rooms were used.

A member of staff told The Herald on Sunday: “They [tenants] rent it on a tenancy agreement and they pay the rent on that property whether they’re sleeping in that property or not.”

The SNP also rented accommodation at £110 a night from Michael Inkster & Co in Lerwick.

The headline bill for the 42-day campaign was £4620.

But Mr Wills’s return stated “occupancy on rooms used basis was 57.14%”, and so only £2640 was declared. This took another £1980 off the spending.

If the full amount had been included in the return, it would again have broken the legal limit.

Inksters declined to comment.

It is common for parties not to declare the full cost of leaflets if some are unused.

However one election veteran told the Herald they had never come across accommodation costs being discounted, given the bill is for renting a roof regardless of who is under it.

In 2010, the Scottish Tory MP David Mundell was forced to go to the Court of Session to correct an inaccurate spending return in that year’s general election.

The true cost of his spending had been around £500 over the legal spending limit.

Highlands & Islands Labour MSP Rhoda Grant said: “The SNP have serious questions to answer over their by-election spending returns.

"The strict rules governing elections are there to ensure a level playing field exists.

"Any break of these rules would erode public trust in politics further.

"Peter Murrell and Nicola Sturgeon need to come clean over the SNP's spending."

A Scottish Conservative spokesman added: “The process for submitting these expenses exists so that there is complete transparency on what political parties spend on trying to win elections. Any discrepancies within the SNP’s submission should be fully probed by the Electoral Commission.”

An SNP spokesman said: “The SNP has an exemplary record in complying with electoral law.

“The idiotic and ill-informed claims of political parties who are serial offenders in breaking the law and have had to pay tens of thousands of pounds in fines are frankly laughable.”

He said if a candidate pays for an expense it must have a receipt, but if a party pays it is counted as a 'notional expenditure' and does not require a receipt.

He added that parties had to "declare only the element of an item which is used." and added: "An item of expenditure is only an election expense if it is used during the regulated period of an election. Unused accommodation must be deducted for the return to be accurate. In [this case] there was a significant reduction to cover the period which was not regulated (that is before a candidate was selected, and after the election)."