Trade deals between the U.K. and European Union (EU) post-Brexit are likely to be "tough", the head of the World Trade Organization (WTO) told CNBC.
Speaking at the Web Summit technology conference in Lisbon, Roberto Azevedo, the director-general of the WTO, said creating trade deals after Brexit will be "very complex".
"A lot of it will depend on the terms that the two parties will come to. So the U.K. on the one side, the EU on the other side," Azevedo told CNBC.
"As far as the WTO is concerned, we don't come into the picture until those two have decided what the commitments they will have with the other WTO members will be and with each other. Until then, when they come to the WTO and say, 'this is my new list of commitments'…at that point in time we then step in."
"Until then it will be a bilateral conversation that will be very complex."
A so-called "hard Brexit" would be where the U.K. loses access to the EU's single market and defaults back to World Trade Organization rules. In a "soft Brexit" scenario, the U.K. would retain some form of membership to the single market.
While the U.K. continues to be a member of the EU, it is unable to negotiate its own trade deals. But under the scenario of a "hard Brexit", this could change. U.K. trade secretary Liam Fox said earlier this year that Brexit was a "golden opportunity" for Britain to trade with the rest of the world.
The WTO chief said it' was hard to know the outcome of Britain's path to exit the EU but negotiating trade deals will be tough.
"The first thing we need to do is define what a hard Brexit is...I think that the less turbulence you have in this process the better. So if we can maintain the kind of relationship that exists today, so much the better. But that's much easier said than done. It will be a tough negotiation," Azevedo said.