What happens if no Brexit deal is agreed?
Following European Union leaders' rejection of Prime Minister Theresa May's Brexit plan, it looks increasingly likely that the UK will leave the EU without an exit deal.
European Council president Donald Tusk has dismissed Mrs May's blueprint, saying it risked the integrity of the EU single market and the Northern Ireland border.
So what would happen if the UK leaves the EU without a withdrawal agreement?
WHAT IS A NO DEAL BREXIT?
The UK is due to leave the EU on March 29 2019. Mrs May has proposed a 21-month transition period after this date to allow businesses and citizens to adapt to the new arrangements.
However, if no agreement is reached on the UK's withdrawal agreement then there will be no transition period.
If that happened, everything associated with the European Union, including its trade agreements, would end. This would have an immediate impact on citizens and businesses.
The truth is no one really knows the exact details of how a no deal Brexit will affect Northern Ireland. However, here are some possible outcomes.
The border issue - the main sticking point between the UK and the European Union - would remain unresolved.
The Irish, British and EU authorities are all in agreement that there should be no hard border, with visible customs controls at the frontier.
"We will do everything in our power to prevent a return to a hard border," Mrs May said at a press conference yesterday.
However, the UK's exit would make the border an external frontier, meaning that customs and immigration controls would have to be introduced.
There have been suggestions on how to operate such controls, including setting up customs posts miles from the border. However, no suggestion has been greeted with widespread approval.
The situation gets more complex around the issue of a 'backstop'.
The Republic believes that December's 'backstop' agreement in principle between the UK and EU will keep Northern Ireland within the EU customs union if negotiations fail.
However, Mrs May and the DUP are adamant that the north cannot operate under different regulations to Britain.
"It would mean breaking up our country," she said yesterday.
She added: "We cannot accept anything that threatens the integrity of our union".
The UK would leave the EU single market and revert to World Trade Organisation rules. It would have to face the EU's external trade tariffs, meaning that the price of goods could increase as businesses passed on any extra costs to consumers.
Last year, auditor KPMG estimated that the price of certain foods would shoot up in the event of a no deal.
It suggested the cost of pure orange juice (from Spain but bottled in Ireland) and olive oil (from Italy and Spain) would increase by 34 per cent and 30 per cent respectively.
Sausages and butter would see price rises of 20 per cent and 25 per cent respectively.
Once the UK leaves the EU it can start trade negotiations with other countries. However, trade deals are likely to take years to broker which could have a devastating affect on the UK economy.
Without a deal, British passport holders will be considered "third country nationals" when travelling in the Schengen area of 26 European states. These states, including France, Germany and Greece, have abolished passport controls at their mutual borders.
British citizens will effectively have the same status as citizens from countries including the United States and Canada. This means passports must be valid for three months after the date of travel.
Irish passport holders will retain the same rights as they do now if they fly from airports in the Republic. However, controls may become more complex for Irish passport holders who wish to travel to the EU from airports in the north.
Irish and British citizens can travel between both countries under the Common Travel Area agreement - part of which dates back as far as 1923.
Britain's Department for Exiting the EU has already confirmed that Irish citizens living in the UK "would have additional rights if they travelled to other member states, but would not have additional rights relating to their lives in the UK".
There is continued uncertainty over the future of more than three million EU citizens, including a large Irish community, who live in Britain.
Mrs May yesterday reiterated to these citizens: "Even in the even of no deal, your rights will be protected".
Flights between the UK and EU could be stopped because both ends of the journey would not be covered by the necessary safety checks.
Ryanair chief executive Michael O'Leary has already warned that flights could be grounded for weeks if no Brexit deal is agreed.
He said if the UK crashed out, flights would need to be cancelled a month before March's withdrawal.
"We are selling tickets between the UK and Europe ... on flights that may not take place."
A no deal is also expected to affect ferry crossings and the Eurostar train which links southern England to mainland Europe.
French minister Nathalie Loiseau has previously indicated trains would be barred from Europe if no exit agreement is reached.
MOBILE ROAMING CHARGES
People with UK mobile phone contracts have surcharge-free roaming in EU countries under EU law.
In the event of no deal, that agreement would expire.
Exiting the EU without a deal could lead to significantly less university research funding.
It would also mean freedom of movement would no longer apply with implications for EU students and staff.
The UK government has guaranteed funding until the end of the decade for research projects that secured European funding, such as Erasmus+.
However, academics have warned this is not enough. Without a deal, funding streams are at risk and longer term planning will take place without institutions' involvement.
A report warned that Ulster University risked losing about €20 million in EU funding and tuition fees as a result of Brexit.
There is also massive uncertainty around university fees. Irish students could face non-EU fees to attend universities in the north - these are about three times greater than EU charges.
Growing uncertainty since the Brexit vote has already affected the flow of students crossing the border.
In addition, UK and Irish universities collaborate extensively, especially under EU research programmes.
Members of the Royal Irish Academy believe this will be affected - with there being a more negative impact on universities in the north than the Republic.
Institutions in the Republic, however, noted there may be potential to win more EU funding if UK researchers become ineligible.
Dire consequences of a 'no deal' Brexit for healthcare have been forecast with fears of a breakdown in the delivery of life-saving medical treatment on both sides of the Irish border.
Cancer care, children's heart surgery and GP services are among those which have a successful cross-border exchange - with fears that some seriously ill patients in parts of Donegal will be forced to travel extra miles for radiotherapy treatment instead of accessing Altnagelvin hospital in nearby Derry.
Access to vital imported drugs, including insulin for diabetics, as well as price hikes for pharmaceutical drugs made in the Republic has also been singled out as a key concern.
Uncertainty about the future of medical research, health protection and security and 'rare disease' co-operation is ongoing.
Trade unions have also pointed to the serious "red tape" difficulties facing some northern surgeons post-Brexit who trained in Queen's University and require Irish registration.
For some doctors living in border cities such as Newry and who work in hospitals north and south, the pressures they are currently facing in Northern Ireland's embattled health service are so extreme they are considering moving to the Republic in the event of a hard border.
As one experienced Co Down consultant anaesthetist put it: "The health service here is just so, so stretched. The idea of Brexit with passport control and an identity check and a customs check to go a short distance to do a day's work, which is ultimately for patient care, is just ridiculous."