Questions: Date of birth, surname.
Why? To verify you are down for a shot.
Survey: Are any of these things true? (recently tested positive, allergies, etc)
Why? Based on the above they know whether or not they can give you which vaccine (based on what they have in stock).
At this point... assuming you are down for a shot and nothing stops you having one that they have... they will give you the shot. Takes a moment, expose an upper arm of your choice, relax, look the other way. They're doing so many of these it's painless and quick.
Edit: I've had the AstraZeneca first shot a few weeks ago. In my area they seem to be random sampling people and the NHS sent a text message inviting me (even though I'm younger than the national age bands in the news). When I was in the queue I saw some people in their 20s... so different GP catchment areas are going at different speeds. I assume they are random sampling other groups just to ensure the medical centres run at a very high utilisation of vaccinations even if some people are slow to respond or book theirs.