SNP ministers were warned five years ago that they could well miss the 2025 deadline for dualling Scotland’s most dangerous road but kept it a secret, it has emerged.

Official papers obtained by a Holyrood committee show the cabinet was told in 2018 that privately financing the £3billion plan to dual the A9 between Perth and Inverness meant a longer timescale.

They also suggest the project cannot now be delivered until the 2030s and the cost has ballooned to between £4.5bn and £7.2bn, putting a question mark over its affordability.

The Government is already facing a £700m black hole in its capital budget for 2024/25. 

The Scottish Tories said the secrecy around the Government “stinks”, and singled out Michael Matheson for criticism, as he was transport secretary from 2018 to 2023.

Now health secretary, he is currently under investigation for claiming £3000 on his Holyrood expenses towards an £11,000 data roaming iPad bill run up by his children on holiday.

A Government source queried the Scottish Parliament's analysis, but acknowledged the deadline was ultimately missed because ministers did not prioritise finance for the A9.

The SNP first promised to dual 80 miles of the A9 in 11 sections in 2011, when it was costed at £3bn and acknowledged as the biggest infrastructure project in Scottish history.

The road has long been notorious for the number of fatalities which occur along it, many at points where single and dual carriageway sections cross over, with 12 fatalities last year. 

However there were multiple delays and dithering over the funding mechanism and only two sections covering 10 miles have so far been modernised.

In February this year, transport minister Jenny Gilruth finally admitted in parliament that the 2025 timescale was “simply no longer achievable”.

She blamed the failure of the latest contract tendering exercise on external factors including Covid, Brexit, the war in Ukraine, the UK mini-budget and high inflation.

She promised a revised timescale this autumn, but has yet to deliver it.

Now material released by Holyrood’s Citizen Participation Committee, which is considering a petition on dualling the A9, indicates the delays long pre-dated those factors.

The Committee obtained 74 documents provided to Scottish ministers between May 2012 and February this year containing “significant, previously unpublished, information”.

An analysis by Holyrood officials said ministers had “never formally agreed a mechanism” to procure the building of eight of the 11 sections.

Mr Matheson was told in August 2018 that using private finance, which became the preferred option for the bulk of the project, meant the 2025 target date would be “unachievable”.

A paper presented to the full cabinet in November 2018 said the evolving approach “will mean the 2025 timescale is not achievable with the end date yet to be determined”.

A December 2021 discussion paper prepared by officials for Mr Matheson and then finance secretary John Swinney said the “earliest completion date” for a privately financed option would be 2032 and for a traditional public sector option 2034.

The former would cost £7.2bn over 30 years and the latter £4.5bn.

The paper said “both of these options would require re-prioritisation from other budgets and difficult choices about the affordability of other projects”.

In December last year, ministers were given two choices: pause the entire project indefinitely or push ahead with parts of it when budgets allowed. They chose the latter.

Tory MSP Graham Simpson said: “The charge sheet keeps growing against the scandal-ridden Michael Matheson.  

“This damning report exposes that when he was SNP transport secretary, he was fully aware that his government were never going to dual the A9 by 2025 – yet he covered this fact up.

“This secrecy in this SNP government stinks and the now-health secretary is at the heart of further deceit.

“Everyone who relies on the A9 feared the route would never be dualled in the SNP’s timeframe, but ministers shamefully only confirmed as much earlier this year.

“Even now, they still haven’t delivered an update on the A9 which they promised would come in the autumn. Their snail-paced progress has cost lives and this report lays bare their cover-up.

“No wonder the campaigners and rural-based Scots who depend on the A9 have lost all trust in this SNP Government.”

Jackson Carlaw, the chair of the Committee, added: “The evidence we’ve received is stark, revealing a piecemeal process, with concerns raised repeatedly about spiralling costs and delays to completion.

“It’s evident that the Scottish Government have known for a considerable length of time that the 2025 deadline was in jeopardy, however it’s less clear what action ministers have taken to address this.”

He said the committee will review the evidence when it meets on December 20, and consider whether to take evidence from Transport Scotland officials and previous ministers.

In a written submission to the committee, First Minister Humza Yousaf, himself a former transport minister, made clear his “continued determination to see the A9 dualled”.

He described upgrading the entire road to dual-carriageway as a “vital part” of Scottish Government efforts “to support the residents and businesses in the Highlands”.

He added the work was “also of national economic importance to Scotland”.

A Transport Scotland spokesperson said: "The advice provided in 2018 related specifically to the impact of moving to a Mutual Investment Model [private finace].

"It did not relate to a traditional capital funding model. It was in late 2022 that Transport Scotland knew with certainty that the 2025 date could not be achieved.”

The Government is expected to updat e parliament on the programme for completing the remaining sections in the coming days.