The politically explosive issue of fisheries could become an early flashpoint in trade negotiations between the European Union and the United Kingdom after it leaves the EU on Friday.

The UK leaves at midnight central European time – nearly four years since the referendum.

Brexit Transition Period

The Brexit transition is a period agreed in the UK-EU withdrawal agreement in which the UK will no longer be a member of the EU but will continue to be subject to EU rules and remain a member of the single market and customs union.

The aim is to allow the UK to continue its current relationship with the EU while the future trading relationship and security cooperation is negotiated.

UK Prime Minister Boris Johnson has said he will not extend the transition period beyond Dec. 31.

EU and UK negotiators have agreed to use their best endeavors to conclude and ratify their new fisheries agreement by July 1, 2020 in order for it to be in place in time for use in determining fishing opportunities for the first year after the transition period.

Should no free-trade deal be agreed to by the end of the this year, it could leave seafood importers and exporters once again scrambling to make preparations for the imposition of tariffs on their products.

Earlier this month EU Trade Commissioner Phil Hogan was widely reported as saying that he expects there to be trade offs with the EU seeking concessions on fishery access and the UK is keen to achieve concessions on financial services in the EU market.

It's on these issues that Anand Menon, professor of European politics and foreign affairs at King's College London, said both sides could be on a collision course when talks begin in early March.

"Financial services and fisheries are not easy, and its not obvious that there will be an agreement on them, and if the European Union as looks likely says actually we want to get these out of the way first then there aren't any quick wins in view," he told the Scottish parliament's Culture, Tourism, Europe and External Affairs Committee last week.

Charles Grant, director of the Centre for European Reform, expects the EU to play hardball over fish, meaning it could become "the first and nastiest part of the entire negotiation."

While only around a third of EU member states care about fish, post-Brexit negotiations on the issue may turn into a test of solidarity with the likes of Denmark, France and Spain for some European nations, even for landlocked ones such as Hungary and Poland with smaller fishing fleets.

"I have been told by some member state governments that they will not agree to any deal on anything unless the British give in on fish quite quickly," Grant told the same parliamentary committee.

"I have heard a senior person in London, part of the government, say we may have to give in on fish...we may have to give the EU access to our waters or we won't get anything for the city of London."

The iconic fisheries debate

Despite financial services being valued at a reported nearly 170 times more and employing more than a million people compared to an estimated 8,000 people in fishing, fisheries was a totemic issue for campaigners wishing to leave the European Union.

While British fishermen were among the most vocal Brexiteers, Andrew Duff, a visiting fellow at the European Policy Centre, said massive delusions were peddled in the referendum campaign about sovereign waters and the "Britishness" of fish.

These delusions completely missed the point about the need for reciprocal market access and the need for common European action to preserve stocks, in the former Member of the European Parliament's view.

"An unpopular deal will be done with the French, the Danes and the Spanish, as it is every year, but this time Whitehall and Edinburgh and not Brussels will have to take the rap," Duff said in a discussion paper earlier this month.

"The government must hope that the wider public will not be paying much attention to the detail of a post-Brexit rumpus on fish."

Scotland's fishing sector pushing hard

To underline the pressure the UK government is facing, the Scottish Fishermen's Federation (SFF) trade body chimed in this week insisting that failure by the government to gain full control of access to UK waters in the next phase of Brexit negotiations would be a “colossal betrayal” of the fishing industry,

"If we are to secure the benefits that leaving the Common Fisheries Policy will bring, the sea of opportunity that lies just over the horizon, the UK must have sovereignty over who catches what, where and when in our waters," SFF Chief Executive Elspeth Macdonald said.

At the same time, the Scottish industry says it never wanted to deny EU vessels the opportunity to fish in UK waters after Brexit.

Dominic Walsh, policy analyst at center right think tank Open Europe, said he believes differences between the UK and EU are exaggerated with much of the talk of the UK's reluctance to allow EU fishing boats access pitted against the EU's desire to keep everything unchanged.

"It will be quite a tricky political fight in the negotiations" Walsh told IntraFish.

"But ultimately there is a potential landing zone for an agreement there."

The automatic right of EU vessels to fish in British waters, under the EU’s common fisheries policy (CFP), will end under a fisheries bill submitted to lawmakers this week.

But the bill is already coming under fire from campaigners who say proposed legislation does not do enough to protect dwindling fish stocks and leaves too many loopholes open.