I don't understand what there was to negotiate about which apparently was done better by the UK than the EU when these vaccines are being sold without profit; so for a fixed price? If there subsequently is a shortage in production you can not accept extra money to provide more to one than the other (then you would make a profit) so I'd say it logically follows that you either go with a first come first serve distribution or a social, per capita, distribution.

PS: I was really hoping the world would have banded together to develop all vaccines publicly; sharing their recipes and allowing the whole world to produce as much vaccine as possible without artificial financial limitations.