Essentially whether the UK contract has been fulfilled is pretty black and white where the EU one is significantly less so.

See below:

> "The level of specificity is partially due to the legal systems they're based on. The U.K. contract is written in English law, which will judge whether both parties delivered the goods based on the exact wording of the contract. The EU contract is written in Belgian law, which focuses on whether both parties tried their best to deliver the goods and acted in good faith.

It's these extra details that give the U.K. more leverage to ensure its contract is delivered effectively. While both contracts say all parties will make their “best reasonable effort” to deliver the vaccine, the U.K. government is clearer in asserting its oversight of the agreement.

This core difference, according to a lawyer familiar with the development of the U.K. text, can be chalked up to the fact that the contract sealed with London was written by people with significant experience of purchasing agreements, specifically drug-buying deals. The European Commission’s contract, by contrast, shows a lack of commercial common sense, in the lawyer’s view.

The starkest example of this difference is a clause in the U.K. contract stating that if any party tries to force or persuade AstraZeneca or its subcontractors to do anything that could hold up the supply of the vaccine doses, the government may terminate the deal and invoke what appear to be punishment clauses — although these are largely redacted. "[1]

https://www.politico.eu/article/the-key-differences-between-...