Guy Verhofstadt told the Standard that the British needed a cross-party agreement and to put “country before party” prior to seeking an extension of Article 50.
“Why should the EU27 even consider a Brexit extension this week, if the UK parliament vote on the deal is cancelled?” he demanded. “Where are the cross-party talks?
“I will keep saying this; it is time for country to come before party. A minority of Right-wing populists cannot be allowed to drive European citizens and businesses off a cliff.”
Mr Verhofstadt is co-ordinator on Brexit for the European Parliament, which has the right to veto any Brexit deal. His warning contrasted with European Council president Donald Tusk, who last week said that he was personally “open to a long extension” if Britain wanted time to “rethink” the whole idea.
There are divisions in the EU over what to do if Mrs May asks for a postponement without getting Parliament to agree a deal.
Mr Tusk is hoping that the UK will hold a second referendum to reverse its decision to leave, and believes a long extension would help.
French president Emmanuel Macron sees a maximum of one month, while Germany’s Angela Merkel is said to favour up to a year.
Mr Verhofstadt and most leaders in the parliament agree with Mr Macron that it should be a month at most.
Diplomatic notes from a meeting of EU ambassadors seen by the Standard say Britain must leave by June 30 or else hold elections to the European Parliament, or the European institutions could be open to legal challenges.
The documents state that “the prolonged presence in the EU framework of a withdrawing state leaves the European Union and its other member states in a legally unstable situation”.