EVEN after 16 years of service on nuclear submarines, this mission was amongst the strangest Feargal Dalton had ever undertaken – bringing to life a sub-sea murder mystery that would become a major television event.

And it would also see critics turn their fire on programme bosses for making the Dublin-born SNP councillor and anti-nuclear campaigner their naval consultant on Vigil, the BBC hit with the superstar cast and politically-charged content.

Created by the team behind police procedural Line of Duty, Scotland-set Vigil shared its leading man, Greenock’s Martin Compston, and similar themes – duty, service, deception, corruption. But the drama also took on geopolitical themes, taking viewers into “Dunloch” naval base and the nearby peace camp and ­looking at threats posed even in ­peacetime and with billions of pounds of warheads at your ­command. “We’re not at war,” Suranne Jones’ DCI Amy Silva, the fish out of ­water amongst seasoned submariners, tells HMS Vigil’s Commander Neil ­Newsome, played by Paterson Joseph. “That is an illusion,” he replies. “We have ­always been at war.”

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More than 10 million people watched every episode and, having launched a thousand articles covering everything from costumes to what would really happen in the case of a murder on a nuclear submarine, the show has certainly created waves.

Some of them related to Dalton’s role as naval adviser. Jackie Baillie MSP, whose Dumbarton constituency includes Faslane, the real-life home to the UK’s Trident fleet, told the Sunday Telegraph newspaper that “the BBC should have employed an expert who, unlike Mr Dalton, is not so ­obviously biased against nuclear submarines and has a long standing association with CND”.

Ex-LibDem leader Menzies Campbell, a member of the House of Lords International Relations and Defence Committee, said that while he could understand “why you might have someone opposed to Trident as an adviser for the peace camp scenes... it would be strange if such an ­individual was giving advice about technical and on-board issues”.

“The World Productions team consulted a range of advisers and experts to make Vigil, including Mr Dalton who had no editorial input but offered factual insight from his long career as a member of the Royal Navy’s Submarine ­Service,” the BBC responded.

READ MORE: 'Panicky' Union flag-wavers plumb 'new depths' over Martin Compston's Vigil drama

One week after the final ­episode screened, Dalton, who sits on ­Glasgow City Council, is reflecting on the drama. The reactions of ­Baillie and Campbell, he says, came as “a major surprise”.

“They have turned a highly respected and popular TV drama into an ­issue about Scottish ­independence,” he goes on. “This is was an ­unexpected but very welcome bonus to my involvement with HMS Vigil.”

Dalton’s role on the production was simple, if not simply done – ­advise the programme-makers about the realities of life on board a Royal Navy submarine, but without giving away any information that would compromise national security. There was no politics in his role, both sides agree, and he wasn’t responsible for the script.

When he got the email from the team, he thought it was a request for an interview. “I said, ‘is this a documentary?’ They said no, it’s a whodunnit on a nuclear submarine and I thought, ‘fantastic’. It ended up being one of those life experiences I wouldn’t ever have thought of having. It did bring me back to my time in the service. I started having dreams I was back on patrol on the real thing.”

A former lieutenant commander, the accomplished engineer served as a Weapons Engineer Officer and fired a missile off the US coast on a training exercise in 2009. He left the service in 2010 to spend more time with his young family and wife Carol Monaghan, who is now the SNP MP for Glasgow North West, and became a physics teacher, a councillor and the convener of the Nuclear Free Local Authorities Scotland Forum (NFLA).

Before this, he served aboard two boats, as they’re referred to in the Submarine Service – the Vanguard-class HMS Victorious and HMS ­Vigilant. Like the fictional HMS Vigil, both “disappear” on regular ­patrols, their coordinates unknown for national ­security reasons.

“I was very careful that I didn’t say anything I knew was of a sensitive nature,” Dalton says – nothing “Vladimir Putin would look to get his hands on”.

“I went back on Twitter for the craic of this programme and I know some people said ‘that’s not what it’s really like’, but you could say that about Casualty or Taggart. I know there would have been lots of submariners screaming at the telly, but from a security point of view, you don’t want to show what it’s really like. The Submarine Service is known as the ­silent service for a reason.”

The National: CND protesters on Michaelson Road Bridge

DALTON is used to criticism. The Fianna Fail member got it for his Irish republicanism before this latest wave, with a petition calling for his removal over claims that he was unfit for office. But he says the comments from politicians over his fitness for the Vigil role are a far cry from the attitudes he found in the Royal Navy.

He’s also used to questions around his anti-nuclear stance, given his previous employment. Dalton says nukes are “despicable” and he didn’t join the navy to work with them. Before retiring, he’d driven Monaghan to CND rallies. “Some people believe there is a British route to nuclear disarmament,” he says, “But as someone who worked within the British nuclear weapon programme and delivered it, I know there is no British route. The only way we will rid Scotland of nuclear weapons is through Scottish independence.

“An increasing proportion of UK defence spending is on nuclear weapons, to the detriment of conventional capabilities and our defence. So along with the compelling moral argument, there is a defence argument for ­nuclear disarmament.” He goes on, “It’s a fascinating thing, the engineering that goes into launching space rockets from under the ocean. It’s Joe 90, Thunderbirds stuff. It’s cutting edge technology, whether you agree with having nuclear weapons or not.

“The armed forces is full of people who believe in Scottish ­independence. I’m an Irish republican, the ­Royal Navy knew and didn’t care so long as I was going to do it by democratic means. A lot of people who don’t know the armed forces will probably think someone from my background would have a cold reception, it was actually the opposite.”

VIGIL, he says, “seems to have gone down an absolute storm with people”. He didn’t know how it was going to end, but says he was “happy with the outcome”.

“The aim of the programme was to be entertaining, it wasn’t a documentary,” says Dalton. “Artistic ­licence was applied throughout. If you wanted to view a documentary, that would have been a whole different programme.

“The reality of life on a Royal Navy submarine is much calmer, more ­professional.

“I’m happy to say that in my 15 years service, I never experienced a fraction of what you saw on the ­programme. The public can be ­assured that the drama Vigil was ­facing is not happening every day.”