I've just read the Telegraph article and they say that the mass vaccination roll out starts in the first week in January using sites at football stadia etc. This will be using the Oxford/Astra Zeneca vaccine as currently four million doses are reported to be ready but Astra Zeneca have said they can produce a further fifteen milion doses in days (I reckon they are producing them already as it is clear it's going to be approved). Regardless of the relative efficiency rate compared to say the Pfizer vaccine the Oxford vaccine had no-one hospitalised or dying in any age group even if they did get Covid. There is also evidence (not proof yet) that it reduces transmission, which would be very significant.
Regarding vaccine orders, the government had to spread the risk as no-one knew which vaccines in development would work and they have done a great job actually in picking winners. Obviously having a UK option is a huge advantage so it's going to be full steam ahead in a couple of weeks. Health centres, pharmacies, hospitals, drive through sites and so on will get through the most at risk groups very rapidly.