The U.K. and 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. “The U.K. and the U.S. 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 Michel had got it wrong.

Is the U.K. blocking vaccine exports?

No. The U.K. government has the power to block all sorts of exports, including some medicines — but has repeatedly stated it hasn’t 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,” 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, Michel suggested there were “different ways of imposing bans or restrictions” on vaccines and medicines.

A European Commission spokesman distanced himself from Michel’s remarks on Wednesday, saying “we know that different countries have got different measures in place — this doesn’t concern vaccines, as far as we understand, coming from the U.K.”

Is the EU blocking vaccine exports?

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

But internal EU documents obtained by Bloomberg show 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 1 million in the past week alone.

Why isn’t the U.K. exporting more shots?

Johnson’s officials say it’s not up to them. European production of Pfizer Inc.’s vaccines — the first to be approved by regulators — is centered in Belgium and Germany. AstraZeneca’s shot is the only U.K.-produced vaccine currently being administered to patients in Britain. But the Astra doses are also manufactured in other countries, too.

British officials point out that the drugmaker has developed a decentralized 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 U.K. is driven by the contractual obligations suppliers like Astra have to their customers, the government says.

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

What does the row say about the U.K.-EU relationship?

It’s 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 program is far outpacing the EU’s rollout 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 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, David Frost, to take charge of the relationship.

One key question still to be resolved is what access U.K.-based financial services will have to the EU market. Separately, the bloc is threatening legal action against London for unilaterally ditching rules on checks on goods crossing into Northern Ireland from the rest of the U.K.

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