No, this isn't FUD. AZ wasn't lying. Yes, it's true that the EU signed one particular contract one day before the UK on August 27. However, the UK had a binding contract with AZ since May already.
"However, the key lies in an earlier agreement that AstraZeneca made back in May with the U.K., which was a binding deal establishing “the development of a dedicated supply chain for the U.K.,” an AstraZeneca spokesperson said."
"However, the key lies in an earlier agreement that AstraZeneca made back in May with the U.K., which was a binding deal establishing “the development of a dedicated supply chain for the U.K.,” an AstraZeneca spokesperson said."
This quote is from this article: https://www.politico.eu/article/the-key-differences-between-...