None of that is really relevant. Both AZ and EU agreed to this contract. If AZ has signed a contract that they cannot fulfill, then they have commited a fraud.
Fraud implies bad faith which I expect is a long, long way from the truth.
The EU is acting like it has first call because of its size as a bloc.
Sorry, that's not how it works. Not forgetting they broke the Good Friday agreement to try and force the point.
The fact that the vaccine was developed in the UK and is produced in the UK can not be an argument. In light of the UK's reliance on the EU vaccine, all this does is show the UK contract with AZ as ethically deficient.
After all, the EU is currently the only supplier for the UK for the Pfizer vaccine - the one that kickstarted the UK's early success. How would the UK's vaccine program look now, if the EU had acted similarly from the start?
Sure, the EU could have mandated exactly this last year. But they shouldn't have. It would have been wrong and morally despicable.
The EU SHOULD now deal with their choices with grace. They don't, which is the real shame.
But if you are British and feel smug about your government's cunning, then I seriously doubt your moral compass.