There may be only 30 million doses of a particular vaccine ordered, but the UK has ordered 380 million doses of various vaccines in total. Some of that will be hedging bets in case some of them don't turn out to work, but I don't think there's any suggestion that particular groups won't be vaccinated. Though given the scale of trying to vaccinate the whole population, undoubtedly some of the more vulnerable groups will be targeted to be vaccinated first.
Exactly. It's also worth saying that you don't need to vaccinate everyone to significantly cut down the spread of covid-19. If you vaccinate 50% of the population, and another 15% have protection via previous infection (which at worst seems to result in reduced likelihood of getting it again) then you significantly reduce infection rates for all as there are far fewer vectors.