A dispute between the Scottish Government and one of Scotland's best-known advertising firm will be a "test case" of the competence of Scotland's public procurement process, industry sources claim.

The Edinburgh-based Newhaven agency is challenging its longstanding client the Scottish Government over its exclusion from the Marketing Services Framework, a list of approved suppliers employed to communicate public-sector messages to the public. The case is set to come before judges at Edinburgh's Supreme Court later this month.

The Sunday Herald understands Scottish Government officials have approached other advertising agencies for affidavits detailing the negative effects of the delay caused by Newhaven's challenge to the new framework, prior to the case coming to court on May 28.

Neither Newhaven nor the Scottish Government would comment on the specifics of the case, though a spokesman for Government said: "Scottish ministers have received a legal challenge from one of the unsuccessful bidders on the new multi-lot marketing services framework. The legal challenge prevents the award of all lots on the new framework, and Scottish Procurement and Commercial Directorate is currently considering legal advice."

Sources familiar with the case said: "The Government will paint Newhaven as bad losers who are challenging because they didn't get on the framework. But even if they don't win in court, it will be worth it if they can put on record their evidence that the Scottish procurement officials have made mistake after mistake after mistake in this process, and have not lived up to standards of transparency, clarity and accuracy demanded by European procurement rules."