Tusk warns of 'dangerous blackout' in Brexit debate

He was referring to comments by pro-Brexit Tory MP and former London mayor, Boris Johnson, who had said in a Telegraph interview that both the Nazi leader and Napoleon had failed at unification and the EU was "an attempt to do this by different methods".

"Such absurd arguments should be completely ignored if they hadn't been formulated by one of the most influential politicians of the ruling party," Tusk said.

"Boris Johnson crossed the boundaries of a rational discourse, demonstrating political amnesia. In some sense, he illustrated a state of mind and emotions of many Europeans, not only from the UK. In no way, however, can this be an excuse for this dangerous blackout."

The council president added that the only alternative to the EU was "political chaos, the return to national egoisms, and in consequence, the triumph of anti-democratic tendencies, which can lead to history repeating itself".

Danish prime minister Lars Loekke Rasmussen denied that Denmark would seek to follow Britain out of the EU in the event of a victory for Johnson's Leave campaign in the British referendum on 23 June.

"I want to be very clear that Denmark belongs within the European Union. It is a core Danish interest to be a member of the EU," said Loekke Rasmussen, refusing to give any details of his possible strategy in case of Brexit.

Europol limbo

Tusk and Loekke Rasmussen held a short meeting to discuss the refugee crisis and how to follow up on a Danish referendum in December in which voters rejected a plan to abandon Denmark's long-held opt out from EU justice and home affairs policies.

The no vote means Danes refused to allow supranational control of its policing and other legal issues.

This has left Denmark in limbo with Europol, the EU's police agency, which gains new powers from 1 May 2017 and formally becomes a supranational body rather than an intergovernmental one.

It is unclear how Denmark can continue cooperation with Europol.

One idea is to secure a parallel deal for future Danish participation in the police agency, but both Tusk and Loekke Rasmussen said any such arrangement would "not be easy".

"The European Union would of course prefer to keep Denmark as close to its core as possible," Tusk said.

"At the same time, we must also respect the outcome of national referendums as well as the existing political and legal limitations."

Loekke Rasmussen said: "I hope that political understanding of Denmark and the rest of Europe - a common interest in counter-terrorism should lead to a situation where we can overcome the difficulties."

The Danish PM said a solution to the Europol issue was needed over summer or early autumn.

Following his short Copenhagen visit, Tusk and the Danish prime minister set off to visit Greenland for two days.

Greenland is not a member of the European Union and is so far the only country to have left the bloc, which happened in 1985 following an in-out referendum.