The EU briefed on the basis that they doses were intended for the UK, there's no doubt of that as it can be read in literally every story about the '29 million dose cache', not just an Italian Scum equivalent. Even the use of the word 'cache' is clearly designed to be emotive and set a specific narrative- it was clandestinely and deliberately hidden- since it was used instead of a neutral word. There was zero evidence that that was true, all they had was speculation and a desire to make anyone apart from them the villain of the piece.
Let's be frank here.
Fundamentally, the EU could have ordered AZ vaccine earlier than the UK did and avoided all of this, but they didn't. That's the core issue, everything else is window dressing- or faecal matter thrown at a fan.
Not ordering early was a deliberate, calculated position made 100% voluntarily by the EU and in retrospect, but also to many at the time, utterly stupid*. They only ordered AZ doses after Sanofi had failed, and well after the UK had ordered theirs. If Sanofi had succeeded and AZ failed would the EU let the UK queue jump to cover up their failure? Not on your fricking nelly; they'd be snickering into their sleeves about the rosbifs backing the wrong horse and how terribly terribly tragic it was that the UK wasn't in the EU any more so missed out. The EU deliberately gambled with their strategy and lost; now the toys are coming out of the cot and they're resolved to fix things by threatening to just grab as much of the stake as they can back unilaterally.
How did they gamble? They tried to cheap out by not ordering enough doses under the belief they could leverage better deals, and they backed the wrong horses for something like 350 million doses worth; and having done that they've whined like nothing else in existence in the hope that they'd be allowed to queue jump over the UK that ordered 100 mln doses, early. They're now threatening to steal doses on the basis of 'fairness'. Fairness that would never in a million years have been in evidence if the roles were reversed. To quote the great philosopher Scott Steiner again: "no simpy". 100% a crisis manufactured in the EU, by the EU. To be fair, partly by bad luck, but then they were also the only bloc that managed to back two losing horses for the large majority of the vaccines they ordered because they were European. Ironically the only successful Euro vaccine is one most people think is actually American...
*even if Sanofi and CureVac succeeded (on time for CureVac, since at least it recently passed Phase 2 unlike Sanofi) they'd still only ordered enough doses for 1 per citizen. And if you're altering reality to make them succeed then that reality might have the BionTech vaccine not work in which case they're down 100 mln doses again. OTOH we've ended up with 4 doses per citizen here, despite having no covid, because we ordered early from multiple vendors. The EU could have done that but they cheaped out, so now they'll just steal other countries' vaccines while still claiming the moral high ground.