The U.K. government told the European Union Monday that it will trigger Article 50 on March 29, officially kicking off the process to exit the bloc. This means that U.K. and EU officials will have until the 29th March of 2019 to agree on how the U.K. will leave the Union and how they will trade in the future.
But such negotiations will be complex and the two-year deadline might not be enough. As a result, U.K. officials have already approached the World Trade Organization to see what they can do in case they cannot reach a deal within the two-year deadline.
"British officials have worked with a number of people in the Secretariat, including Director-General Roberto Azevêdo, who have explained a wide range of WTO rules including things like independent schedules in goods, services and agriculture and how these schedules could come into being," Keith Rockwell, spokesman for the WTO, told CNBC via email.
"They have also explained Article 24," he added.
Article 24 refers to the section of the WTO agreement on tariffs and trade that allows trading partners, in this case the EU and the U.K., to implement an interim agreement while they are negotiating a new trade arrangement. This would mean that the EU and the U.K. could continue discussing Brexit beyond 2019 and for as long as necessary.
The article states that any interim agreement should include a schedule for a new free-trade area "within a reasonable length of time" – but it doesn't determine what is reasonable. According to Politico, this could last for 10 years and still be considered "reasonable" – pushing Brexit until 2029.
"Importantly, both the UK and the EU would have to agree on this," Keith pointed out.
It is in the EU's interest to ensure good trading relations with the U.K., but according to an international official, who didn't want to be named due to the sensitive topic, in Brussels there is one clear mandate for the negotiations: "Brexit has to be worse economically than staying in the EU."
Such an approach could have an impact on agreeing on an interim deal.
It's not the first time that a "transitional" deal has been mentioned but this has always been followed by other controversies.
"My view is that it will take longer than (the two years)," the Irish finance minister, Michael Noonan, told CNBC on Monday.
"I think that everybody now even though they haven't stated it openly are…I would envisage a transition period," he added.
Though it would give more time to both negotiating sides, EU officials claim that the U.K. would have to continue paying into the EU budget and being subject to rulings from the European Court of justice during that time – but these are two of the reasons why Brexiters want to leave the EU rapidly.
"An interim deal is what many people involved in the Brexit preparatory talks have been suggested, and not just for trade. There will need to be a longer time for the U.K. to dismember itself from the EU and a transition deal can include all exit issue plus trade," Fredrik Erixon, director of the European Centre for International Political Economy told CNBC via email.
He added that the U.K. is likely to get away with a 10-year deal at the WTO. "I don't think there are many countries that would have anything critical to say of such a deal as they would be helped by it," he added.