More than a quarter of the United Kingdom’s fishing quota is in the hands of a tiny group of the country’s wealthiest families, an Unearthed investigation has found.

Just five families on the Sunday Times Rich List hold or control 29% of the UK’s fishing quota.

The finding comes from a new Unearthed investigation that traced the owners of more than 95% of UK quota holdings – including, for the first time, those of Scotland, the UK’s biggest fishing nation.

It reveals that more than two-thirds of the UK’s fishing quota is controlled by just 25 businesses – and more than half of those are linked to one of the biggest criminal overfishing scams ever to reach the British courts.

Meanwhile, in England nearly 80% of fishing quota is held by foreign owners or domestic Rich List families, and more than half of Northern Ireland’s quota is hoarded onto a single trawler.

The news comes as the government is preparing to publish a new fisheries bill, which will set the legal foundations for the UK’s fishing industry after Brexit. But while the government is hoping it can net access to more fishing rights in the Brexit negotiations, it has said the new bill will not see any redistribution of the UK’s existing quota rights.

As Unearthed’s investigation reveals, this would leave the bulk of UK fishing rights in the hands of a small domestic elite and a handful of foreign multinationals.

Responding to Unearthed’s findings, shadow environment secretary Sue Hayman said ministers needed to take “urgent action to use the powers that they have domestically to redistribute fishing quota to deliver a fairer deal for smaller boats”.

“Fishing was the poster child of the Leave campaign and [environment secretary Michael] Gove has already broken promises he made to the industry to secure full control of our waters during the transition,” she continued. “With all the talk of ‘take back control’, ministers have the power to distribute UK quota now and put the smaller-scale fleet first. So why wasn’t it mentioned in their white paper?

“This [Unearthed story] shows that, while it points the fingers at others, this government is to blame for a sector rigged in the interests of the super-rich. Any future fishing policy must consider how new and existing quota can be more fairly distributed and we will treat this as a priority in the upcoming fisheries bill.”

The investigation found: