I'm pretty sure the EU invested more in the AZ vaccine in total over the course of things. Honestly, this just seems to be petty "We want the vaccines so we can vaccine non risk groups" while the EU needs to vaccinate their risk group. The Tories have used the vaccine program to divert from the hide their corruption and incomptence.

A cursory Google search implies that the EU did indeed invest quite a lot of money on the AZ vaccine roll out, mid-August, after it had already entered trials which had been part-funded by the UK government months earlier.

The EU investment appears to amount to a deposit on actual vaccine doses, and a sum to ensure that dose costs are kept at cost until the pandemic is over - rather than a support of the development itself, which appears to have mostly born by AZ itself, the UK government and Oxford university. The UK has since spent billions (about £3Bn?) on AZ Vaccine procurement, a figure which dwarfs the EU's spend on the same (I think it's something like EUR360M?).

As much as I dislike politics and am disgusted by some of the costs - especially around PPEs last year (which seems to have been much abused) - I find it easier to believe that there was a lot of panicked flailing and a gamble on vaccines as a way out of this mess that would allow the UK to get started back up ASAP, which they're now reaping, rather than using the current mess as a distractionary political football.