Guy Verhofstadt, who is the European Parliament’s lead Brexit negotiator, described the vote as a “disaster” for the EU, claiming it is important for all parties to reach a successful arrangement.
Theresa May attended her final EU summit before she is expected to trigger Article 50 of the Lisbon Treaty, afterwards spelled out her desire to get down to business and begin Brexit negotiations with Brussels.
Mr Verhofstadt, however, warned his European Parliament colleagues will have the power to veto any deal between the UK and EU which is presented to them.
Speaking on BBC Radio 4’s Today programme, the Belgian politician said: “The fact that a big country like Britain is leaving the European Union, I think the most negative fallout from this brexit referendum has not been, for now, economically.
Guy Verhofstadt mourned a European Union 'crisis' caused by Brexit Theresa May's most powerful quotes Fri, March 10, 2017 Play slideshow Getty Images 1 of 8
'I will be ruthless in cutting out waste, streamlining structures and improving efficiency'
“The important fallout has been geopolitically, it has showed a crisis in the European Union – it is a disaster!
“Anyway, Britain going out of the European Union in my opinion is tragic, disaster and catastrophe.
“But it is also responsibility, the responsibility to find a new relationship between the UK and European Union.
“Unfortunately, the decision taken by the UK Government it cannot be the single market – they don’t accept the four freedoms – it cannot be the customs union because they want to make their own trade deals, it cannot be the European Court of Justice, it cannot be the European Economic Area.”
The best pictures from EU Summit 2017 Fri, March 10, 2017
EU leaders will gather for a two-day summit to discuss a number of issues including Great Britain's exit from the Union
Play slideshow AFP/Getty Images 1 of 18
Hollande and Merkel on the second day of a European Summit
The negotiator added he wishes to see a good deal reached between the UK and Europe, allowing them to continue a working relationship.
In the wide-ranging interview, Mr Verhfostadt hinted at the possibility of a transitional deal being put in place while the full divorce settlement is reached.
“We have to make an attempt for this to be ready by November, at the latest, December of this year,” he added.
“If we don’t have a withdrawal agreement, possibly some transitional arrangement and we are going to use the transitional agreement to further detail this future partnership.
“Let’s not be, ‘It will take two years.’ In total, it will take two years plus the whole period of the transition to sort out partnership between the UK and European Union.”
Mr Verhofstadt also claimed he will give individual Britons the opportunity to keep hold of the EU citizenship.
The MEP claimed he had received over 1,000 letters from worried Brits pleading with him to allow them to keep their freedom to travel freely around the Continent.
“All British citizens today have also EU citizenship. That means a number of things: the possibility to participate in European elections, the freedom of travel without problem inside the Union,” he said.
“We need to have an arrangement in which this arrangement can continue for those citizens who on an individual basis are requesting it.”