EU Brexit negotiator Michel Barnier deplored a lack of progress in the latest round of post-Brexit trade talks on Friday, accusing Britain of stalling negotiations.

Barnier reported his concern at the end of a week of negotiations, which came amid the added urgency of the coronavirus pandemic that has shattered the economy in Europe.

"To tell you the truth.. the objective that we had for tangible progress, this objective has only been partially achieved," a testy Barnier told a news conference after the talks.

"The United Kingdom did not want to engage seriously on a certain number of fundamental issues."

Britain left the European Union on January 31 and both sides have until the end of the year to forge a new basis for relations, barring an extension that Barnier confirmed London still refuses.

It's not going too well, according to the EU side
It's not going too well, according to the EU side AFP / JOHN THYS

"We need real progress by the month of June if we want to find a deal by the end of the year that meets the level of our interdependence and our geographic proximity," Barnier said.

Britain "cannot refuse to extend transition and at the same time slow down discussions on important areas," he added.

In its response, London called the discussions "full and constructive" but also said there had been "limited progress in bridging the gaps between us and the EU".

"The UK remains committed to a deal with a Free Trade Agreement at its core," Downing Street said in a statement but noted there were "significant differences of principle in other areas".

The trade talks entered high gear with a first round in March, but quickly fell victim to the COVID-19 crisis when Barnier and his UK counterpart David Frost both tested positive for the virus.

Talks were suspended for six weeks as each side focused on the deadly virus and explored ways to hold the talks that involve more than 100 negotiators on each side.

'We need real progress by the month of June'
'We need real progress by the month of June' AFP / François WALSCHAERTS

The lack of progress will feed fears that no deal will be reached by December 31, meaning that WTO rules with high tariffs and customs barriers would come into force between the UK and EU.

That prospect is especially alarming given the cataclysmic recession already facing the continent that cross-Channel chaos would only make worse.

But British Prime Minister Boris Johnson, who has been hospitalised because of the virus, refuses to be swayed, with his government insisting that the current deadline must stand.

Unacceptable for Johnson is that an extension would also prolong the so-called transition period, in which Britain must obey EU rules and regulations during the course of negotiations.

The thorny topics remain as they have been from the start of talks: fishing and maintaining fair and open trade standards, known as a "level playing field".

London is trying to negotiate a series of packages in different domains including fishing, goods, aviation, justice and energy. But EU leaders want a single overarching accord.

The thorny problem of fishing rights alone -- hugely important to several key EU states, notably France -- could derail the whole process.

"There will be no agreement on a trade deal without a deal on fishing. That should be crystal clear to the UK," Barnier said.

London criticised the EU's insistence on maintaining existing fishing quotas.