The British Government is withdrawing the UK from an arrangement that allows foreign countries to fish in British waters, it has announced.
Ministers will trigger withdrawal from the London Fisheries Convention, signed in 1964 before the UK joined the European Union, to start the two-year process to leave the agreement.
What is the London Fisheries Convention?
The convention allows vessels from Ireland, France, Belgium, Germany and the Netherlands to fish within six and 12 nautical miles of the UK's coastline.
It sits alongside the EU Common Fisheries Policy which allows all European countries access between 12 and 200 nautical miles of the UK and sets quotas for how much fish nations can catch.
Why is the UK government withdrawing the agreement?
Ministers claimed the move would help take back control of fishing access to UK waters, as it will no longer be bound by existing access agreements, and enable the country to become fully responsible for fisheries management.
UK vessels will also lose the right to fish in the waters six to 12 nautical miles offshore of the other countries.
How will it affect Ireland?
The decision by the British government to withdraw the UK from the London Fisheries Convention could "wipe out" the Irish fishing industry.
According to the CEO of Irish South and West Fish Producers Organisation, Patrick Murphy, the long-term impact could be "catastrophic" for fishermen and women.
The move will mean that trawlers from the Republic of Ireland will no longer be allowed to fish within 12 nautical miles of the UK coastline.
"If this full withdrawal goes ahead, it could wipe out the Irish fishing industry," Mr Murphy told the Irish Independent.
"If you take, for instance, an average day last week where we would have taken in just over 200,000 tonnes of product, 100,000 of that would have been coming from English waters.
"We disagree with this withdrawal fundamentally, we will suffer the most."
Francis O'Donnell, CEO of Irish Fish Producers Organisation, said that Northern Irish fishermen would be the "big losers" in the withdrawal.
British ministers will trigger withdrawal from the London Fisheries Convention, signed in 1964 before the UK joined the EU, to start the two-year process to leave the agreement.
Mr O'Donnell said that the withdrawal was an "early indication of what to expect" in the aftermath of Brexit.
Howth Fisherman Shaun Doran told RTE's Morning Ireland that he wasn't expecting the UK to withdraw the agreement "so soon".
"There has been talk in the industry that the UK is going to pull some things out of the hat but this is a surprise. I wasn't expecting it so soon.
"The UK just flexes its muscles to see what reaction it's going to get and how far it's going to go. Fishing is an old industry but we'd like to see our guys doing something similiar. I know we don't have any convention but we'd like to see our guys saying 'hold on a minute'. We've talked around the issue for years but nothing tangible has ever happened. We want a serious piece of our industry back."
He added that the fishing industry is being used as a pawn in the wider economic negotations.
"We're a fragmented industry because we've so many different types of fishing. No one fisherman can elect a TD so we're not important in Dail Eireann. We're not a huge industry but we're a very important industry."
Shaun O'Donoghue, CEO of Killybegs Fisherman's Organisation told RTE's Morning Ireland that the UK is "determined to have a hard Brexit".
"I wasn't surprise but when it comes to fishing, the UK is determined to have a hard Brexit.
"The access that really matters to us is the immediate line between us and the UK.
"We as an industry have been lobbying the minister and the former Taoiseach and we got a commitment that fisheries would be a priority in the negotiations, especially as fish swim freely between the UK and Irish waters."
Mr O'Donoghue said that it's important not to separate the fishing negotiations from the trade negotiations.
"On average we need 30 per cent access to UK waters. We're dependent in the UK waters for fish such as mackarel. If the UK decide that we will no longer be able to access their waters, there will be significant job losses across the country. Everybody will be affected. This has to become a priority. We're in a very vulnerable state."
How has the world reacted to the decision?
Environment Secretary Michael Gove said: "Leaving the London Fisheries Convention is an important moment as we take back control of our fishing policy.
"It means for the first time in more than 50 years we will be able to decide who can access our waters.
"This is an historic first step towards building a new domestic fishing policy as we leave the European Union - one which leads to a more competitive, profitable and sustainable industry for the whole of the UK."
Barrie Deas, chief executive of the National Federation of Fishermen's Organisations, said: "This is welcome news and an important part of establishing the UK as an independent coastal state with sovereignty over its own exclusive economic zone."
The UK fishing industry was made up of more than 6,000 vessels in 2015, landing 708,000 tonnes of fish worth £775 million.
Some 10,000 tonnes of fish was caught by other countries under the convention, worth an estimated £17 million.
Will McCallum, Greenpeace UK head of oceans, warned that pulling out of the London Convention would not alone deliver a better future for the UK fishing industry.
"For years, successive UK governments have blamed Brussels for their own failure to support the small-scale, sustainable fishers who are the backbone of our fishing fleet," he said.
"If Brexit is to herald a better future for our fishers, the new Environment Secretary Michael Gove must keep the 2015 Conservative Party manifesto commitment to re-balance fishing quotas in favour of 'small-scale, specific locally-based fishing communities'."
Environmental law firm ClientEarth consultant Dr Tom West said the move appeared to be an aggressive negotiating tactic.
"As a country outside the EU we need to consider how we can best co-operate with our neighbours rather than unilaterally withdrawing from all agreements in the hope that standing alone will make us better.
"Many fish stocks in UK waters are shared with our neighbours and so need co-operation and shared management."
He also warned of the need to put in place strong laws to protect marine wildlife, or there was a risk the UK would row back on hard-won environmental protection over the last 40 years.
Ben Stafford, head of campaigns at WWF, said: "Achieving sustainable fishing is about a lot more than which country fishes where.
"It is about ensuring that fishermen use the right fishing gear, that fishing takes place at levels that maintain sustainable stocks and that we pioneer ways to monitor what is happening at sea in order to understand the impacts of fishing.
"Leaving the EU means we could get these things right, but we will still need to co-operate with our neighbours, as fish do not recognise lines on a map."
Scotland's Fisheries Secretary Fergus Ewing said: "The UK Government's decision to withdraw from the London Fisheries Convention is a move we have been pressing for some time now.
"Our priority is to protect our fishing industry and allowing unrestricted access to our waters to remain through this convention clearly would not be doing that.
"We cannot rely on the UK Government to do that, having regularly put the interests of fishing communities elsewhere in the UK ahead of those in Scotland.
"It is vital therefore that all powers over policy be repatriated to Scotland and current EU funding for fisheries be matched and transferred to Scotland in full."
How will it impact the EU free trade deal?
Labour's shadow environment secretary Sue Hayman said the "provocative" move could risk talks on a free trade deal.
"Labour opposes a hard Brexit that would jeopardise jobs, environmental sustainability and the future prosperity of the British fishing industry," she said.
"The London Convention predates British membership of the EU by a decade and has arguably been superseded by the Common Fisheries Policy which the UK will withdraw from automatically following our leaving the EU.
"Given that the majority of fish caught by UK vessels are within the Atlantic (fishing area 27) which includes the edge of Greenland to North Russia and as far south as the bottom of Spain/Portugal, it is vital that any Brexit deal does not jeopardise access to these waters for our British fishing fleet.
"This provocative decision at this stage of the negotiations puts at risk those necessary and far more valuable fisheries management arrangements we will need to agree on leaving the EU as well as a tariff-free trade deal so vital to our British fishing exports. It is another example of the Tories' reckless approach to Brexit."