First Minister Alex Salmond has been summoned to give evidence next week in a £3.5 million case against Scottish ministers due to be heard in the Court of Session.

In a development believed to be unprecedented in post-devolution Scotland, lawyers acting for a Southampton-based road-gritting company have asked the First Minister to take the stand to answer for the Scottish Government's actions, reportedly including the procurement of "emergency" salt supplies from Ineos in Grangemouth.

The case, to be heard before Lord Woolman from May 6 to May 20, concerns Scottish Government agency Transport Scotland's alleged failure to put out to public tender a contract to supply road salt in the harsh winters of 2009-10 and 2010-11.

Nationwide Gritting Services (NGS) claims that, as a result of the alleged breach of the 2006 Public Contracts (Scotland) Regulations, it was the only major gritting company in the UK not to supply Scotland with salt in the years in question.

It claims that this lost opportunity cost the firm £3.5 million in revenues, helped its competitors, and resulted in Scotland overpaying for the product by as much as £5m.

In a preliminary hearing before Lord Woolman last week, Alistair Clark QC, acting for Scottish ministers, cited as defenders in the case, told the court: "The position is that the pursuers have produced a list of questions which they wish to be put to the First Minister.

"The defendant's position is that the First Minister is entirely content to give a statement and to appear as witness in this case. There is no difficulty with that although he has of course an extremely busy diary."

In what appeared to be the opening of a negotiation over the range of questions to be put to Salmond under oath, he said some questions contained "tendentious irrelevancies".

He added that, as the attendance of a minister was "potentially very disruptive of government businesses" he was "seeking assistance from the pursuers" in taking out some of the tendentious material from the questions.

"If the insistence is on asking questions which are nothing to do with the case then it may be that I will have to come back with some revised motion," he said.

NGS is represented by Aidan O'Neill, a Scots QC described on the website of Matrix Chambers as a "leading expert on EU law" whose textbook on the subject is "an essential reference for every legal practitioner in the UK".

The Legal 500 (2012 edition) ranks him as a leading silk at the London Bar in EU and competition law.

The scheduling of a court showdown next week is itself a defeat for the Scottish Government, which tried and failed to have the case dismissed on a technicality.

It said NGS failed to make its complaint within a required three-month period after the discovery of the alleged damage.

The argument was rejected by Woolman, who upheld NGS's claim that the government, via the agency Transport Scotland (TS), had "breached its duty of transparency" in response to a ­challenge, as Scottish bureaucrats had "drip fed" information about contracts after requests by NGS.

TS's more substantive defence is that it was entitled to enter contracts ­without a competitive tendering procedure, including publication in the Official Journal of the European Union (OJEU), as it was exercising an exemption based on "the extreme urgency of the [weather] situation".

A spokesman for NGS told the Sunday Herald: "It will cost us about £250,000 to pursue the case, but things shouldn't be happening behind the scenes where public money is concerned.

"We want to be part of a fair process like every other commercial company.

"There needs to be transparency and accountability in public procurement, which won't happen if everyone shies away from pursuing [cases like this].

"Mr Salmond's evidence is extremely relevant and is somewhat startling as to how procurement is conducted within the Scottish Government. Once the case takes place next week, all will be revealed. We can say nothing further at this stage."

Contacted by the Sunday Herald, neither Professor Robert Black QC, professor emeritus of Scots law at the University of Edinburgh, or James Wolffe QC, Dean of the Faculty of Advocates, was able to cite a precedent for a Scottish minister giving evidence in the Scottish High Court, although neither would say categorically no precedent existed.

A Scottish Government spokesperson said: "The Scottish Government intends to robustly defend its position in this case. Everything Scottish ministers and officials did during two extreme winters was to keep the country moving in exceptionally difficult circumstances. We will be happy to provide any statements the court requires but given the case is still subject to court proceedings, it would be inappropriate to provide further detail or comment at this stage."

Asked to confirm whether or not Salmond would take the witness box in person, as opposed to by video link, the spokesperson added: "We can't discuss how the evidence is going to be presented.

"As mentioned in court, the FM would give a statement and he is prepared to appear if necessary."