Three Indian sailors were detained for working illegally on a Scottish fishing boat, their trade union has said.

The men have now all left the UK voluntarily after being warned that they could have faced potential deportation and 10-year bans from entering the country, according to the International Transport Workers’ Federation or ITF.

The deckhands, who entered the country legally on transit visas, spent more than a month in custody after being picked up by immigration officials back in May.

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The ITF said the men had signed contracts to work in international waters – but had ended up serving off the coast of Britain and even in port. That meant they should have had skilled worker visas.

The union accused the men’s employers, Oban-based The Star Fishing Company, of breaching immigration rules.

“Time and time again we see migrant workers paying the cost for the UK’s broken immigration system,” said ITF Fisheries’ Section Chair Johnny Hansen.

“We have a case here where three migrant fishers have been thrown in detention for over a month and threatened with severe, life-changing punishments, as a result solely of the action of their employer to fish in UK waters. Yet it is the workers who pay the price for a rogue employer, like The Star Fishing Company, breaking the law.”

The men worked on a boat called The Star of Jura, based out of Oban. The Star Fishing Company is registered at the offices of one of its owners and directors, John “The Dredge” MacAlister of John MacAlister (Oban) Limited.

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The Herald was unable to reach Mr MacAlister. Two years ago John MacAlister (Oban) Limited – which is listed as one of two “persons of significant control” of The Star Fishing Company – was fined £187,000 for illegal dredging off Yorkshire.

Last year one of its skippers was fined just over £3000 for fishing in a Scottish marine protected area. Environmental groups said the penalty was “derisory”.

The industry veteran – the 69-year-old first skippered a boat half a century ago – has previously denied claims from Green groups that his vessels damage the seabed.

Speaking in 2021, he told this paper: “We are not causing the damage they claim. That would be against my interest.”

Mr MacAlister was a former spokesman on scallops – usually called "clams" in Scots – for the Scottish White Fish Producers’ Association, an industry lobby.

The Herald also sought comment from another major shareholder of The Star Fishing Company, Peterhead-based Seafood Ecosse. We received no response. The business last year received a Scottish Government grant of more than half a million pounds.

The ITF cited the fishing offences by vessels linked to Mr MacAllister as they criticised his company. The union’s Mr Hansen also took aim at the Home Office for pursuing its members but not their employers.

He said: “Through no fault of their own these deckhands have now been ‘voluntarily’ removed from the UK with 12-month re-entry ban, a ban which has consequences to their livelihoods and ability to provide for their families. And it’s only because of the ITF that they didn’t get 10-year bans. The unfairness of this is an indictment on the UK Home Office.”

Solicitor Thal Vasishta from Paragon Law, who has been representing the crew, said: “These men have been treated as criminals, not victims, in this situation.

“Across the industry globally deckhands have no control over where a vessel fishes, that is down to the owner and skipper.”

Human rights lawyers have previously railed against Britain’s transit visas for seafarers, saying they offer a “loophole” that can lead to the exploitation of foreign workers.

A Financial Times investigation this summer found half of all deckhands in the British fishing fleet were foreign. The paper said many were paid £1000 a month.

The Orkney and Shetland MP Alistair Carmichael – a former Scottish secretary – told the FT: “We need to have a proper visa system that allows the fishing industry to get the access to the labour that they need and which allows people working in fishing boats to be given the same protections of employment law and health and safety legislation as everybody else.”

A Home Office spokesperson said: "Illegal working causes untold harm to our communities, cheating honest workers out of employment, putting vulnerable people at risk, and defrauding the public purse.

“Illegal working visits are up by more than 50% on last year and arrests have more than doubled, with more people arrested in 2023 than during the whole of 2022 as a result of this activity. We are also removing those with no right to be in the UK.”