John Swinney, the Deputy First Minister, will rely on Audit Scotland to investigate the findings of a television documentary claiming the contract awarded to Ferguson Marine for two ferries was rigged.

He has rejected calls fo police to be called in despite claims by Tory Transports spokesman Graham Simpson that the contract “looks like corporate corruption”.

A documentary drew on leaked documents suggesting Ferguson Marine received preferential treatment in the procurement process, including the option to change the design, and that it obtained a 424-page document from a design consultant setting out the technical requirements, while other bidders had to rely on a more limited 125-page specification.

The yard at Port Glasgow was bought out of administration in 2014 by Jim McColl, but was later brought under public control after costs spiralled and the delivery date was delayed. The management has changed twice after Mr McColl departed.

Both the Conservatives and Labour have called for Police Scotland to be brought in to look into the latest twists in the scandal.

Graham Simpson, the Scottish Tory spokesman on transport, claimed the eventual deal “looks like corporate corruption”, adding: “This alleged rigging of the contract, this potential fraud, has cost the country £250 million and it’s rising.”

Speaking at Holyrood, Mr Swinney said that Audit Scotland would be able to “establish any further inquiry that is required to be undertaken”.

A spokesman for Audit Scotland said it would look at the substance of the allegations, adding that Stephen Boyle, the auditor-general, has the “full support” of John-Paul Marks, the permanent secretary to the Scottish government.

“We will be looking at the substance of the allegations raised around procurement by the programme before deciding if further audit work is required.”

Caledonian Maritime Assets (CMAL), the public corporation which owns the ferries, ports, harbours and infrastructure in the west of Scotland, said in a statement: “The procurement process for the dual fuel vessels contract was subject to an audit by the Scottish Government’s Procurement Services team, and this audit found no issues with non-compliance.”