It's a bit more complex than that. The entire UK procurement strategy with AstraZeneca has been professionally managed and invested in, with contracts locked-down in English law; whilst the EU's has been half-arsed, unprofessional, and contracted in wishy-washy Belgian law. The EU are now desperately trying to save face by pretending the UK's the bad guy when they've really just been utterly shit legally, and completely craven individually in trying to destroy confidence in the AZ vaccine to cover up their failings.
Legally and morally the EU are fucked on this so they either need to fall back on dirty shit tactics like export bans, or come to an agreement with the UK. The latter would likely be possible (no real need to vaccinate 20 year olds in Britain when 70 year olds in France haven't had it) but they've done such a good smear job on AZ that a lot of Europeans don't want that jab now anyway, so the EU look a bit like the bald bloke fighting over a comb.
Good piece on it here.
#benefitsofbrexit