The scandal came to light in 2005, when Scottish officials raided fish factories to uncover “serious and organised” schemes to systematically evade quota restrictions for mackerel and herring, using underground pipes, secret weighing machines, and extra conveyor belts to land 170,000 tonnes of over-quota fish over several years.

A multi-year police investigation followed, resulting in a series of court cases over 2011 and 2012 in which three fish factories and more than two dozen skippers were hit with fines and confiscation orders for “black landings” of undeclared fish.

Unearthed’s investigation found that of the 20 biggest holders of Scottish quota, 13 have directors, shareholders, or vessel partners who were convicted of sea fishing offences in the black fish scandal.

Among those prosecuted were four members of the Tait family – worth £115m according to the Rich List – whose Klondyke Fishing Company is the second-largest quota holder in Scotland.

The four men – all skippers on its vessels – were hit with fines and confiscation orders of more than £800,000 for their part in the scam.

Two years later, one of those skippers, Peter Tait, 50, reportedly bought the most expensive house sold in Scotland that year. Over the past five years Klondyke has paid out shareholder dividends totalling £56m.

Unearthed has reached out to Klondyke but the company declined to comment.

The Scottish top 10 also includes the vessel partnership that runs the trawler Christina S. In 2012, two men involved in that partnership – Ernest Simpson, 71, and his son Allan Simpson, 49, both of Aberdeenshire – were handed fines and confiscation orders totalling more than £800,000 for their involvement in the black fish scam.

Four years later, the Christina S was among the flotilla of vessels that sailed up the Thames with Nigel Farage, to protest EU fisheries policy weeks before the Brexit referendum.

John Anderson is chief executive of the Scottish Fishermen’s Organisation, a huge fish producer organisation which has several members – including the Christina S – that were involved in the black fish scandal.

He told Unearthed: “The pelagic fishermen and processors involved will be the first to acknowledge that, in the past, mistakes were made.”

As a result, he continued, the sector had founded the Scottish Pelagic Sustainability Group to oversee the certification of its main fisheries to Marine Stewardship Council (MSC) standards. Since that time, he added, “98% of the group’s stocks have been certified as sustainable and well managed by the MSC.”

Foreign flagships

In England, the UK’s second largest fishing nation, three Rich List families control around 30% of the quota.

A further 49% is ultimately held by Dutch, Spanish and Icelandic interests who have bought up English vessels and quota.

The most significant of these interests is Cornelis Vrolijk Holding, a Dutch multinational whose UK subsidiary alone holds 24% of English quota, making it the biggest quota-holder in England, and one of the five biggest in the UK.

Matthew Cox, chief executive of North Atlantic Fishing Company, Cornelis Vroljik’s UK subsidiary, said the company had been established in the UK since 1984, employed around 60 UK fishermen, had two UK offices, and had launched a UK apprenticeship scheme. He also suggested that the type of fishing his company does is not well suited for small-scale fishermen.

He added: “North Atlantic does not operate at the expense of small-scale fishermen. Pelagic [midwater fish such as mackerel and herring] and whitefish fishing are very different and a simple comparison/substitution between each is not possible.

“The deep sea nature of the environment make pelagic fishing difficult, dangerous and not very attractive for artisanal fishermen who tend to focus on low volume, high value fish such as cod or monkfish.”

The bulk of the company’s quota is for pelagic fish – which swim at midwater – and it has always emphasised the fact that its nets do not damage the sea bed.

However, after the Brexit vote in 2016 the company bought a beam trawler – with nets attached to a heavy beam designed to trawl for “demersal fish” that are found close to the sea bed – and bought up quotas for plaice and sole.

Mr Cox said: “Following the 2016 decision for the UK to leave the EU it was very clear early on, to the directors of North Atlantic Fishing, that there would be changes to the UK fishing industry. North Atlantic had always focused on pelagic fishing and it was therefore decided that the company should spread its risk in the interests of the company and its workforce and enter the demersal fishing industry in a very limited manner.”

Privatising a public resource

Small scale fishermen told Unearthed that successive governments had mismanaged fishing rights, allowing quota to be consolidated on a handful of supertrawlers while smaller, low impact fishermen had been progressively starved of access.

Jerry Percy, director of the New Under Ten Fishermen’s Association, told Unearthed this had resulted in a situation where the smaller inshore vessels that make up 77% of the fleet had ended up with “less than 4% of the quota”.

“This is privatisation of a public resource,” added Mr Percy, who campaigns on behalf of fishermen with smaller, under-10m long, vessels.

Large scale fishing interests contacted for this piece argued that their businesses generated hundreds of direct and indirect jobs, and that it was misleading to rank businesses by quota holdings alone, when the amount and value of fish that can be landed against those holdings varies between species, and area, and from year to year.

Several also pointed out that many of the biggest quota holders identified by Unearthed were trawlers focused on midwater pelagic stocks, like mackerel and herring.

These fisheries, they claimed, were environmentally friendly – with a low carbon footprint and no impact on the seabed – but the fish were too low-value and far from the coast to be attractive to small-scale fishermen.

John Anderson is chief executive of the Scottish Fishermen’s Organisation – a huge fish producer organisation with several of the top 25 in its membership.

He told Unearthed: “While it is true that there has been considerable consolidation within the pelagic catching sector over the past 20 years, with a trend towards fewer, more efficient vessels each with a greater concentration of fishing opportunity, the economic reality is that small-scale, inshore fishermen, many of whom are also members of the SFO, do not have the necessary capacity or markets needed to fully utilise the pelagic quotas that are already available to them.”

Mr Percy retorted: “If you go back years ago, there was any number of smaller inshore boats that were reliant on mackerel and especially herring in the North Sea before the inshore herring fisheries were decimated by overfishing by larger-scale interests.”

Nick Underdown, of the Scottish campaign group Open Seas, said it was hard for smaller boats to take up mackerel quota without investment in onshore facilities to support them. “At the moment, the supply chain infrastructure favours bigger boats,” he told Unearthed.

“But if we invest in processing with the strategic intention to help the smaller-scale fleet, then inshore fishery could bounce back.

“This would be a lifeline for those harbours where fishing has declined due to consolidation.”

A spokeswoman for the Department for Environment, Food and Rural Affairs said: “We are clear fishing communities and our wider economy should benefit as much as possible from those fishing the UK’s quota, and we are working closely with fishermen to review and reform the rules around the economic link condition.”