Sailing majestically under Tower Bridge, it was the flagship trawler that played a central role in Nigel Farage’s Brexit flotilla during the referendum campaign.

The Fraserburgh-registered Christina S was one of several boats used to highlight the benefits to fishermen and local communities from the UK withdrawing from the European Union.

However, the owners of the vessel – Ernest and Allan Simpson – hold more than 3 per cent of Scotland’s entire fishing quota.

Another family, headed by skipper Robert Tait, who bought the most expensive home in Scotland in 2014 for more than £3 million, is worth an estimated £115m. The huge sums have been made by large-scale fishermen, with five wealthy families controlling one-third of Scotland’s total quota, despite the entire pelagic fleet consisting of just 17 vessels.

But for those outside the big companies, fishing is becoming a less and less profitable pursuit due to a quota system that favours larger enterprises over small vessels.

A study by Greenpeace’s investigative unit claims to reveal a vastly unequal system where a minority of wealthy families control huge swathes of fishing rights to the detriment of local fishermen.

In desperation, many small scale fishermen resort to contacting larger outfits, or those they know have Fixed Quota Allocations (FQA) that they do not fish. Those owners can set their own prices and lease out quota, allowing the fisherman to catch more.

The prices set for leasing out FQA can vary by hundreds of pounds. To lease a tonne of cod for example, can cost from £300 to £800. The resulting catch might bring just £1,100 at market, meaning a profit margin of £300 before staff and equipment costs.

According to Greenpeace, the situation has left some fishermen going out on boats alone because they cannot afford to pay a crew, while others have found that, after boat costs, they are still losing money and have stopped fishing altogether.

Jerry Percy, founder of the Under Ten Fishermen’s Association, which represents small scale fishermen, said: “The fish in our seas are a public resource, it’s yours and mine, managed by Government on our behalf. They should therefore never be treated as just another commodity, to be bought and sold to the highest bidder.

“The hoarding of quota risks creating a distorted market in which the price of fish stocks, and access to them, is controlled by just a few companies.”

The problem, say critics, dates back to the 1950s when economists argued that the problem of diminishing fish stocks brought about by fleet expansion and mass industrialisation should be solved by the market.  They proposed that states create a limited right to catch fish that could be bought and sold.

Iceland was one of the first countries to implement this market-based policy in the Eighties. Their fish stocks began to recover and the fishing fleet grew more profitable. But the privatisation of once common fishing-rights led to many fishermen becoming dispossessed as banks started trading in fishing rights and the system eventually crashed.

In the UK, the price of large fishing boats and their associated right-to-fish has rocketed, which has led to many young people being priced out. In many cases only large companies with the backing of banks can buy boats.

Greenpeace hope the UK can succeed where Iceland failed, and rein in the market to create a fairer system.

Will McCallum, head of oceans at Greenpeace UK, said: “How long before the Government stops blaming other countries, looks at its own broken system, accepts responsibility for fixing it and creates a fairer and more sustainable distribution of fishing quota across the UK? With the Fisheries Bill rumoured to be just weeks away, there has never been a better opportunity to do just this.”

A spokesman for Lunar Fishing said: “The quota available to the inshore fleet (top sliced from the pelagic vessels) is more than the under-10m fleet can catch, so there is no merit in the suggestion that there is disadvantage to the ‘small-scale fishermen’.

“In fact the vast majority of fish caught requires larger vessels to catch because of location, depth and weather challenges. It would be impossible for the inshore fleet to catch a small percentage of the quota.

“In relation to workforce, Lunar uses the quota to employ around 600 people in the local communities of Peterhead, Fraserburgh and Aberdeen. Many more are employed in providing services to the company.”

A spokesman for Sir Ian Wood’s fishing arm, the Don Fishing Co and JW Holdings, said: “Both come from strong fish catching backgrounds with Sir Ian Wood’s father, grandfather and great grandfather all being fishermen. The Don operates as a management and fish selling company working on behalf of about 15 vessels in which it has mainly minority shares and another 15 vessels which it helps manage and sell the fish.  The Don Co’s one and only reason for owning some quota itself and helping a large number of fishing vessels to buy their own quota is to enable the vessels to have sufficient quota to be viable.”

A spokesman for Andrew Marr International said: “AMI fully supports robust fishery management including full compliance to protect fish stocks and sustainable fishing. AMI has 10 vessels in the English Fully Documented Fishery Scheme with on board camera monitoring.

“The main stocks that AMI fishes for in the North Sea are cod, haddock, whiting, saithe, monkfish. In these species, the Under 10 fleet have excess quota that they have not used in the last several years.”

A spokesman for Interfish said: “Across our fleet we were the first UK fleet  to achieve full certification against the Responsible Fishing Scheme in 2006 and maintained this against the new standard in 2017 – no  other fleet of skippers have achieved this standard.

“Interfish are active within several MSC client groups enabling sustainable certification of offshore and inshore fisheries.”