@SilverGlitterBaubles
Also are all vaccines given 12 weeks apart regardless?
The recommendation for AZ is between 4 and 12 weeks apart. The NHS are going for within 12 weeks. I think I have seen it said that it can be up to around 16 weeks (I think I saw that 10 - 16 weeks was coming up as the optimum period) and I think they are probably going for within 12 weeks to ensure that if people cancel appointments theres time to chase up / reschedule etc.
The recommendation for Pfizer is 21 days but the NHS is going for between 3 and 12 weeks instead. Pfizer didn't do any research into delayed second jabs so its something of a live experiment thats based on the fact that AZ seemed to actually be better with a slightly longer gap.
I know that a friend of mine who had Pfizer through a GP has been told that her second jab is likely to be somewhat sooner than 12 weeks simply due to the schedule of when the GP is getting deliveries.
So no it doesn't have to be exactly 12 weeks but I don't think you can actively book two doses further apart than that either (unless you've already had one) because the computer won't allow it.
I know someone who got a spare dose and they were told the clinically was fully booked for second jabs for the full 12 weeks but if they checked back the following day when the system was updated and the recond of them having had their first was added then new slots should appear for that clinoc but they could book an alternative venue if they wished.
So I think its slightly nuanced and dependent on how you got your first jab as to when you can get your second.
Anyone who can't book their jab because it won't give them a second slot, should just keep checking as they are being updated and added on a daily basis.