There's A Surprise.

Britain was lying & the EU was telling the truth.

"Best Reasonable Effort" is clearly defined to include supplies from UK based facilities. Along with from facilities from anywhere else in the World.

https://www.euronews.com/2021/01/29/eu-astrazeneca-row-von-der-leyen-hits-back-at-vaccine-maker-saying-contract-crystal-clear

So the Swiss model is not going to have a problem arbitrating there.

Even if the EU still has to live with the shame of subjecting themselves to such things. When they really didn't have to.

Although, as I've said. 

I doubt the EU actually want delivery.  They want a refund.

So they can go and buy the clearly superior Russian vaccine.