The UK faces the prospect of leaving the EU with "no deal" if it "wastes" more time before beginning its Brexit negotiations, the European Union's chief Brexit negotiator has warned.

Michel Barnier, whose department within the European Commission has spent months preparing for Brexit, said: "I can't negotiate with myself ... My preoccupation is that time is passing, it is passing quicker than anyone believes because the subjects we have to deal with are extraordinarily complex," he said in an interview with a select group of European newspapers including The Financial Times.

The interview is Mr Barnier's first since being appointed the European Union's point man on Brexit.

Theresa May's disastrous election result has thrown the Brexit negotiations into question with no clear sense of when they will begin or what sort of Brexit and future relationship the UK is now seeking.

Prior to the election, Ms May had said that the UK would be leaving the single market and the customs union and she repeatedly insisted that "no deal is better than a bad deal."

Since the election, her reappointed Brexit Secretary David Davis, who told Sky News that the negotiation start date may have to be delayed, has said that the "no deal better than bad deal" slogan still stands but said that the government would listen to those calling for a softer Brexit.

However, in his interview, Mr Barnier sounded increasingly impatient with the UK, saying: "I don't know what hard Brexit or soft Brexit means. I read yesterday 'Open Brexit' too! Brexit is withdrawal from the EU - it's the UK's decision. We're implementing it."

The negotiation start date was due to be Monday or Tuesday this coming week but is now likely to be delayed because of the timing of the Queen's Speech, itself delayed because of the Conservative Party's quest to reach a political deal domestically with Northern Ireland's Democratic Unionist Party.

"Next week, it will be three months after the sending of the Article 50 letter," Mr Barnier said, referencing the UK's formal withdrawal notification letter.

"We haven't negotiated, we haven't progressed. Thus we must begin this negotiation. We are ready as soon as the UK itself is ready."