The UK has an agreement for supply with AZ and the EU has a supply agreement with AZ simultaneously.Nah the bold bit is the part where in my view you've gone wrong.
It's not priority, like they've shifted to prefer the UK once issues arose - they haven't. They're simply proceeding with the contracted plan for the UK, as that allocated supply chain was unaffected.
So priority is the wrong word.
If AZ took away from the plan for UK vaccines, they then breach a contract with the UK. Deliberately. They can't do that.
As said, people are 'annoyed' at the EU because they're casting around seeking to blame based on the UK supply chain being unaffected. Which is political.
The EU have a APA to build capacity prior to supply.
The UK supply is being met, the EU supply is reduced by 60% (not being met).
It's not necessarily a political statement to state that the UK supply chain is unaffected. It's evidence that supports a breach in contract between AZ and the EU. If two contracts exist in parallel and capacity for one is met at the detriment of another, then the party adversely affected will of course seek redress.
If AZ can't meet the demand for both, it's a headache for the EU, which will becomes headache for AZ...which may become a headache for the UK.