LONDON (BLOOMBERG) - The United Kingdom and the European Union are trading blows again - this time over coronavirus vaccines.

European Council President Charles Michel started the latest row while making an attempt to defend the bloc from accusations of what he called "vaccine nationalism".

"The facts do not lie," he wrote in a newsletter on Tuesday (March 10). "The UK and the US have imposed an outright ban on the export of vaccines or vaccine components produced on their territory."

That provoked a furious response from the British government, with Prime Minister Boris Johnson insisting that Mr Michel had got it wrong.

Here's a look at the facts of the spat.

Q: Is the UK blocking vaccine exports?

A: No. The UK government has the power to block all sorts of exports, including some medicines - but has repeatedly stated it has not stepped in to stop a single vaccine dose leaving the country.

"Let me be clear, we have not blocked the export of a single vaccine or vaccine component," Mr Johnson told Parliament on Wednesday. "We oppose vaccine nationalism in all its forms."

After the row broke out over his original claim that Britain had imposed an outright ban, Mr Michel suggested there were "different ways of imposing bans or restrictions" on vaccines and medicines.

A European Commission spokesman distanced himself from Mr Michel's remarks on Wednesday, saying that "we know that different countries have got different measures in place - this doesn't concern vaccines, as far as we understand, coming from the UK".

Q: Is the EU blocking vaccine exports?

A: EU member states can block exports, with the approval of the European Commission. Last week, Italy halted a shipment of AstraZeneca shots to Australia.

But internal EU documents obtained by Bloomberg show that the vast majority of shipments overseas - 249 out of 258 - have been allowed. In fact, the EU has sent 34 million doses to other countries, with Britain receiving the most - including one million in the past week alone.

Q: Why isn't the UK exporting more shots?

A: Mr Johnson's officials say it is not up to them. European production of Pfizer-BioNTech's vaccines - the first to be approved by regulators - is centred in Belgium and Germany. AstraZeneca's shot is the only UK-produced vaccine currently being administered to patients in Britain. But the AstraZeneca doses are also manufactured in other countries, too.

British officials point out that the drugmaker has developed a decentralised manufacturing and supply chain, meaning many of the batches destined for patients in the EU are made in the bloc itself.

The movement of vaccines, and their components, into and out of the UK is driven by the contractual obligations that suppliers, such as AstraZeneca, have to their customers, the government said.

AstraZeneca has previously insisted that it is simply fulfilling its vaccine delivery obligations under its various contracts with both the UK government and the EU.

Q: What does the row say about the UK-EU relationship?

A: It is going to be bumpy. The mutual relief when a trade deal was struck on Christmas Eve has given way to a recurrent war of words over a range of issues ever since.

Vaccines became a flashpoint because Britain's programme is far outpacing the EU's roll-out of shots, and European politicians are feeling the heat.

In Britain, too, the government is coming under pressure over Brexit-related disruption to trade with the bloc. While Mr Johnson insists these are just teething problems, his team has stepped up its rhetoric against the EU in recent weeks, and he has appointed a combative new minister, Mr David Frost, to take charge of the relationship.

In terms of both substance and political rhetoric, the spat over vaccines highlights how Brexit is still far from over.