Expert legal advice shows the Scottish Government does not need to put west coast ferry services out to tender, Labour has claimed.

The party used a debate at Holyrood to argue the Clyde and Hebrides ferry services could be exempted from a process which could see routes change hands from publicly-owned CalMac to private firm Serco.

The Scottish Government insists it is required to tender for the contract in order to comply with European Union (EU) law.

Earlier, members of the RMT union campaigned outside the Scottish Parliament for the services to remain in public ownership.

David Stewart, Labour MSP for the Highlands and Islands, attacked Serco's record, questioning whether it was a "fit and proper" company to run public services.

"The idea we should trust Serco to operate these lifeline public services is deluded, dangerous and absurd," he said.

Mr Stewart pointed to legal advice provided to the RMT by EU procurement law expert Gordon Nardell QC that the Scottish Government could use a provision known as the "Teckal exemption" to avoid putting the service out to tender.

He said: "The minister continues to argue that the government have no choice but to put these ferry services out to tender, that it's all the fault of the regulations enforced by faceless European Commission bureaucrats.

"But independent observers and the trade union movement do not agree with this meek surrender of our national interest is either necessary or desirable.

"Over the summer I headed to Brussels, I met with commission officials who advised me that ferry regulations do allow for the Teckal exemption to be made should conditions of public ownership be met. I believe that Calmac meets the Teckal criteria.

"Our purpose today is to stop the tender process dead in its tracks and award the contract to Calmac."

Transport minister Derek Mackay said: "It is our opinion that we have to undertake this process and you cannot escape from it.

"Breaking the law is not an option, it would leave the Scottish Government open to challenge because of those European rules and that would be a challenge to taxpayers and the services themselves.

"The current tendering exercise is no different to that undertaken by the previous Labour/Liberal Democrat administration when they decided that it was a legal requirement to tender the current contract in 2005."

Liberal Democrat MSP Tavish Scott, a former transport minister, recalled the day his former government lost a vote seeking Holyrood's endorsement for its proposal to tender a previous CalMac contract in line with EU law.

"It was exactly the same position then as it was now," he said.

"So, on that point I agree entirely with Derek Mackay, but the only point I will take slight issue with is that the role reversal is fairly entertaining.

"At that time Fergus Ewing, leading for the SNP, said: 'We will not tender.' He went on to tell us that when the SNP takes power: 'We will not tender'."

Former SNP minister Bruce Crawford said: "When the SNP was in opposition we opposed what is going on today.

"We were wrong then because we can see the circumstances now. They're wrong now on the Labour benches."

Conservative MSP Alex Johnstone said the debate appeared to be taking place "in a time warp back to the 1970s".

"The nature of this discussion so far has gone back to the good old fashioned 'public good, private bad, no privatisation at any cost' approach," he said.