The UK is a small country. Their "Britain first" clause, in absolute terms, has little impact.
If the EU had done the same with the Pfizer/BionTech vaccine, then the only countries with any vaccination success would have been the US, the EU, and whoever made a deal with either China or Russia (assuming efficacy there).
The EU has a moral obligation to supply the world, given that the BionTech vaccine was the first to be available and still is the one with the highest success rate.
So, personally, I am glad that the EU did not follow the UK with an exclusivity contract. It would have been a literal disaster for many countries, including the UK.
I am less happy about the EU's reaction. There is really nothing to be done right now, AZ played the UK and EU against each other. The EU should remember this - and also the UK's "Britain first" contracting very well indeed. However, this grandstanding and sable-rattling is unbecoming and will accomplish nothing.
Several British people, even here, don't even acknowledge that the overwhelming success of the UK's vaccine efforts are in large part due to a vaccine funded, developed and produced in the EU, and the EU's unwillingness (or inability) to prioritize its own population. In turn, they also don't acknowledge the qualitative difference of the UK's priority contracting with their own vaccine.
Lacking such perspective, how would one perceive the idiocy that the EU now perpetrates?
What is happening now is a diplomatic disaster. The EU should have just published the numbers of how much vaccine was sent elsewhere, how much of the vaccine successes are due to doses produced in the EU, how the "trade balance" of vaccines looks between different countries (say with the UK), and how the EU's deficient vaccine program can be seen in that light.
Then, the reader could eventually draw their own conclusion about the moral and ethical behavior of certain countries in a global pandemic.
No matter what AZ did, cutting large parts of the world off from the main supply of the most efficient vaccine is still not justifiable. And threatening this is simply absurd. Yet, the EU commission did just that.
That's the shameful part.
The naive contracts are not, at least not in the bigger picture.