They will not hold back half of the vaccine for the second dose.That would use up the initial supply of 400,000 vaccinations (2 doses per person) and I haven't seen any news of further deliveries just that they are expecting Millions before the end of the year.
There will be 4 to 5 million vaccine doses in the UK by the end of the year.
They aren't publishing daily delivery schedules.
They didn't even publish details of the initial 800,000 doses other than to say it was expected in the UK on a particular day.
The lorries you saw on telly leaving the factory and heading for the UK were not full of UK vaccine, they were just random lorries leaving a busy factory.
The government didn't say how they were getting here or how they would arrive or where they were being taken.
That will remain the case.