Fears are growing that a no-deal Brexit could lead to serious disorder at sea and possible loss of life – which could then trigger a wider escalation of tensions.

Britain’s leading expert on international fisheries law believes that, following a no-deal Brexit, there would be “a real risk” of serious violence breaking out between British and EU fishermen, many of whom depend on access to UK fishing grounds for their economic survival.

“A toxic mix of historical grievances, real and perceived unfair treatment, and, in some cases, a lack of clarity about legal rights is bound to result in fishing disputes,” Professor Richard Barnes of the University of Hull told The Independent.

“Together with inflammatory newspaper headlines, broken political promises and broken livelihoods, we will have all the ingredients for violent confrontations at sea,” he said.

“This is likely to be part of the reality of a no-deal Brexit."

Nigel Farage joins 'Fishing for Leave' flotilla campaigning for Brexit Show all 10 1 /10 Nigel Farage joins 'Fishing for Leave' flotilla campaigning for Brexit Nigel Farage joins 'Fishing for Leave' flotilla campaigning for Brexit A Fishing for Leave pro-Brexit "flotilla" makes its way along the River Thames in London PA Nigel Farage joins 'Fishing for Leave' flotilla campaigning for Brexit Boats from the 'Fishing for Leave' campaign group join a flotilla along the Thames River Getty Images Nigel Farage joins 'Fishing for Leave' flotilla campaigning for Brexit Supporters of the EU Remain camp attach banners to Tower Bridge as they await a flotilla of fishing boats campaiging for Brexit to pass under the bridge AFP/Getty Images Nigel Farage joins 'Fishing for Leave' flotilla campaigning for Brexit A Fishing for Leave pro-Brexit "flotilla" alongside HMS Belfast (left) as it makes its way along the River Thames PA Nigel Farage joins 'Fishing for Leave' flotilla campaigning for Brexit Bob Geldof (centre) on board a boat taking part in a pro-EU counter demonstration PA Nigel Farage joins 'Fishing for Leave' flotilla campaigning for Brexit A flotilla of fishing vessels campaigning to leave the European Union REUTERS Nigel Farage joins 'Fishing for Leave' flotilla campaigning for Brexit A boat from the 'Fishing for Leave' campaign group and smaller boats from the 'In' campaign join a flotilla along the Thames River Getty Images Nigel Farage joins 'Fishing for Leave' flotilla campaigning for Brexit A fishing boat campaiging for Brexit passes by the Tower of London AFP/Getty Images Nigel Farage joins 'Fishing for Leave' flotilla campaigning for Brexit A boat decked out in flags and banners from the 'Fishing for Leave' campaign group Getty Images Nigel Farage joins 'Fishing for Leave' flotilla campaigning for Brexit Fishing boats campaiging for Brexit pass under Tower Bridge AFP/Getty Images

“When fishermen from either the UK or continental Europe feel that they have no other option, they have, in the past, shown that they are willing to take matters into their own hands if their rights or interests are threatened,” he said.

“Given that the UK lacks the practical capacity to fully enforce fishing law in all its waters, this is a significant risk.

“History shows us that fishing disputes can quickly escalate. Any close quarters situation between fishing boats, let alone deliberate ramming or physical violence, can result in injury or even loss of life,” he said.

The leader of one of Britain’s major fishermen’s organisations is also warning of potential problems ahead.

Jeremy Percy, director of the body representing the UK’s small (under 10-metre long) fishing vessels, the New Under Ten Fishermen’s Association, fears that differences in interpretation of international law are likely to result in French and other EU fishing vessels, supported by their governments, seeking to continue to fish in UK waters after Brexit, despite potentially being prohibited by Britain from doing so. His association represents 80 per cent of UK fishing vessels.

In the event of a no-deal Brexit and any consequent lack of a fisheries deal, Mr Percy fears that tensions could lead to “clashes between UK vessels and those continental European vessels that have traditionally fished in British waters”.

“Clashes at sea would be a highly undesirable and very dangerous development,” he said.

“We should not forget that there was a serious clash in the English Channel over scallops less than a year ago – and clashes of that sort in British waters can therefore not be discounted in the event of a no-deal Brexit,” he said.

The scallops confrontation in late August 2018 took place off the Normandy coast and involved 35 French and five British vessels. French boats deliberately collided with two British crafts and a UK vessel collided with a French boat. The pitched battle involved the use of rocket flares and the throwing of petrol bombs, stones and metal objects at English and Scottish vehicles.

By pure good fortune, there were no injuries – but three British and three French vessels were damaged, including one UK ship which the French succeeded in setting on fire.

Last month, Didier Guillaume, the French minister of agriculture and food, who also has responsibility for the French fishing industry, said that French fishermen would continue to fish in UK waters, even in the event of a no-deal Brexit.

“It is possible that, with Boris Johnson, we will have a hard Brexit. There is no circumstance in which one could prevent, in which Boris Johnson could prevent, French fishermen from fishing in British waters,” he said.

In the event of a no-deal Brexit, key aspects of international fishing law are likely to be perceived in different and contradictory ways by different countries.

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On the one hand, the Common Fisheries Policy (under which continental and British fishermen are currently allowed to fish in each other’s waters) would cease to apply if Britain leaves the EU without a deal.

On the other hand, leaving without a deal merely means that fishing in UK waters will be mainly governed by the United Nations Convention on the Law of the Sea (Unclos) – the principal international authority on all maritime matters.

The UK government has promised that Brexit will give Britain back control of its waters – but, in the absence of a deal, Professor Barnes thinks that that “may well be, in practical terms, an undeliverable promise”.

The problem is that the UK does not have enough patrol boats and fisheries protection vessels to adequately police all its territorial and exclusive economic zone waters – and therefore, in effect, mainly depends on international negotiation and agreement to control who fishes in its waters.

Between the EU and non-EU countries, fisheries negotiations and agreements are carried out between the European Commission and the relevant external country.

Unfortunately, the UK government has made it clear that, in the event of a no-deal Brexit, it will not start paying the previously agreed £33bn 'divorce settlement’ it owes the EU. And the EU has made it equally clear that, post Brexit, no negotiations on any future trading relationships (including fishing) can begin until the UK starts to settle its debt.

In such deadlocked circumstances, there will inevitably be a political vacuum in which fishing chaos could reign.

France and other EU states will take the view that, because their fishermen have legally fished in UK waters for decades, custom and practice allows them to continue. Indeed the concept of custom and practice does feature in the law of the sea.

The UK will argue that, without an agreement, continental European fishermen cannot fish in UK waters – and that too is featured in international law.

France and others are likely to counter by claiming that their fishermen are entitled to fish in UK waters if there is a surplus of fish, which there certainly would be, given the relatively small size of the UK fishing fleet and given what will almost certainly be its reduced ability to sell its fish to its neighbours. The concept is touched upon in Unclos.

Theoretically, the French or other continental European governments could threaten to take the UK to the international Law of the Sea court in Hamburg – but in practice, it is unclear as to whether they would actually be able to do so.

The British government has repeatedly promised to take back control of UK seas (both territorial waters and exclusive economic zones). In the absence of any deal, Britain could only attempt to do that by trying to prevent French and other EU fishermen entering UK waters.

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“Partly because of a substantial shortage of appropriate Royal Navy vessels, that would certainly be a challenge,” said Professor Barnes.

The UK’s exclusive economic zone waters extend for up to 200 miles from the UK coastline and cover 282,808 square miles (three times the UK’s land mass). However, to cover that vast area, the UK currently only has nine vessels and will have just four more by May 2020.

Four of the current nine are operated by the Royal Navy in English and Welsh waters on behalf of the Department for Environment, Food and Rural Affairs. The others are operated by the Scottish Government – and by Northern Ireland.

Although the Royal Navy vessels are armed with 20mm cannon and machine guns, it is very unlikely that they would be deployed against unarmed fishing vessels. So it is unclear exactly how the Navy would be able to force large numbers of potentially very defiant continental European fishing vessels out of British waters.

EU fishing vessels have traditionally fished in most of the UK’s exclusive economic zone waters and parts of its territorial waters for decades, indeed in some cases for hundreds of years – especially in the Celtic Sea (West and South West of Pembrokeshire and Cornwall) and in the English Channel.

The North Sea, the Irish Sea and the Atlantic to the west of the Hebrides also attract substantial numbers of EU fishing vessels. Many are likely to continue to fish in all these waters, despite the UK banning them from doing so, in the event of a no-deal Brexit.

Tariffs in the event of a no-deal Brexit Show all 15 1 /15 Tariffs in the event of a no-deal Brexit Tariffs in the event of a no-deal Brexit Pork There will be tariffs on pork in order to protect British farmers Getty Tariffs in the event of a no-deal Brexit Cheese There will be tariffs in place on some cheeses including €22.10/100kg of cheddar, €19.10/100kg of processed cheese and €18.60/100kg on some blue cheeses Getty Tariffs in the event of a no-deal Brexit Milk There will be no tariffs in place on milk Getty Tariffs in the event of a no-deal Brexit Car Parts There will be no tariffs on car parts imported from Europe PA Tariffs in the event of a no-deal Brexit Cars However finished cars will face tariffs of 10.6% Getty Tariffs in the event of a no-deal Brexit Alcoholic drinks There will be no tariffs on alcoholic drinks - except on some rums due to ingredients used in their distilling process Getty Tariffs in the event of a no-deal Brexit Beef There will be tariffs on beef in order to protect British farmers Getty Tariffs in the event of a no-deal Brexit Fish There will be no tariffs on many types of fish including cod, haddock, salmon and sea bass Getty Tariffs in the event of a no-deal Brexit Fruit and vegetables There will be no tariffs on almost all fruit and vegetables Getty Tariffs in the event of a no-deal Brexit Chocolate There will be no tariffs on chocolate or other cocoa products Getty Tariffs in the event of a no-deal Brexit Poultry There will be tariffs on poultry in order to protect British farmers Getty Tariffs in the event of a no-deal Brexit Ceramics There will be some tariffs in place on ceramis Getty Tariffs in the event of a no-deal Brexit Steel There will be no tariffs on steel Getty Tariffs in the event of a no-deal Brexit Coal There will be no tariffs on coal Getty Tariffs in the event of a no-deal Brexit Lamb/Mutton There will be tariffs on the meat of sheep in order to protect British farmers Getty

Particular hotspots are likely to be in the English Channel and in the Celtic Sea – and potentially in disputed waters between Northern Ireland and the Irish Republic. These latter areas – Lough Foyle and Carlingford Lough – will be of particular political sensitivity. In both locations there are rich fisheries in areas where the sea border between Ulster and the Republic have never been agreed.

Up till now, the UK and the Republic have both been members of the European Union and have operated under the Union’s Common Fisheries Policy – but after 31 October, those areas would find themselves in a legal vacuum in a potentially fraught border-related political situation.

So far, Lough Foyle and Carlingford Lough have not widely featured in the Brexit debate – but that could well change.

But the Channel and the Celtic and other seas – and the Northern Ireland-Republic sea border loughs – are not the only places where fisheries-related problems could escalate.

As soon as the UK government tries to prevent continental European fishermen from continuing to fish in UK waters, French (and potentially other continental European fishermen) are likely to blockade UK fish (and possibly other) exports to continental Europe by physically stopping UK refrigerated trucks as they attempt to drive inland from continental Channel ports.