LONDON, March 28 (Xinhua) -- As Britain marks the first anniversary of triggering the mechanism leading to it quitting the European Union (EU), a leading British expert said it would take an unexpected blow or catastrophic happening to reverse Britain's decision.

In a recent exclusive interview with Xinhua, Professor Iain Begg, with the London School of Economics and Political Science (LSE), said he believed Britain would have eventually decided to leave the EU, even without the referendum called by former prime minister David Cameron.

SHOCK RESULT

Begg, a professorial research fellow at the LSE's European Institute, underlined Cameron was fulfilling an election pledge, but even the leave campaigners were stunned by the shock result.

On March 29 last year, Britain handed a letter to the European President Donald Tusk triggering what is known as Article 50, the so-called irreversible article to start the process of ending its membership of a trading bloc it joined in 1973.

Prime Minister Theresa May told MPs in the House of Commons hours later it was a moment for the country to come together. A new word was added to the English dictionary, Brexit -- six letters that sum up Britain's intention to part company from its 27 neighbors in the EU.

The past year has witnessed bitter political battles between politicians in the leave and remain camps. There have been calls for a re-run of the 2016 referendum when Britain voted by a 52-48 margin to quit Europe, an unexpected result that continues to send shockwaves around the world.

IRREVERSIBLE ACTION

With recent talks between British and European negotiators paving the way for a negotiated agreement on a future trading relationship, the big question for the coming year is whether it is too late to reverse Brexit.

Begg said he would sum up the past year as one in which Britain made concessions, adding this was something he had expected.

"There were initial red lines drawn by May, stating things Britain was not going to budge on, and this was unrealistic," said Begg.

What has emerged in the past year as a potential deal breaker is the question of the Irish border, added Begg.

The republic of Ireland joined the EU at the same time in Britain 45 years ago. It meant there was no need for a land border between Ireland and Northern Ireland. Britain leaving the EU will create the only UK-EU land border between the two parts on the island of Ireland.

Begg described the border situation as a "trilemma", with three options.

"If Britain exits from the customs union there would need to be a border between Northern Ireland and Ireland. It is basic logic," said Begg.

"There is a potential fudge but it would still mean a breaking of the Belfast Agreement which restored peace to Northern Ireland after decades of troubles.

What has been settled is the question of citizens' rights, the status of Europeans in Britain and British people in the EU post-Brexit. A transition or implementation period will continue until December 2020 to give both sides time to reach a permanent trade deal.

QUESTION OVER FINANCIAL SECTOR

"What it does not resolve is we don't yet know if the UK will accept what is on the table. What it also leaves is the future of Britain's financial services," added Begg.

"A trade deal is all about the movement of goods and tariffs; there is no concept for financial services."

Although there is talk of regulatory equivalents, Begg senses there is no real willingness at the moment by the EU to give Britain the full access it wants. But there is talk of regulatory equivalents

The final answer will determine the future status of Britain's vital financial services sector, one of the country's biggest money-spinners.

The concern, said Begg, is whether Britain will be bypassed with institutions setting up in Frankfurt or elsewhere.

Michel Barnier, the EU's chief Brexit negotiator, has made the point of saying no existing EU trade deal has a model to cover Britain's financial sector.

"The UK's view is saying: well, let's invent one," added Begg.

"The financial business in Britain has created jobs, more than in any other country, and anything that hit that would be damaging to the UK. It is also a major exporting sector with a high net surplus (invisible exports), and it is also a major contributor to Britain's public finances," added Begg.

Also at risk without a good deal would be complimentary services, such as accountancy, law and consultancies.

Begg said there were latent risks that could undermine the size of the sector and the scale of its exports.

"There are now two and three quarter years to negotiate a new trade deal which is not a lot of time in historical terms," said Begg.

He described as pretty well certain that Britain's exit from the EU would continue, with a final divorce coming in December 2020.

"I can't see a pathway to stop it. It would take 326 MPs to vote for a new referendum in the House of Commons. It is hard to see, as it would have to be done within months for an act of parliament to take place. To do that by March, 2019 is implausible," said Begg.

"It would take something dramatic, something like a wild card that has not been anticipated."