@Shaun *******
The recommendation is for the second jab to be after 3weeks (Pfizer), 4 weeks (Moderna) and 4-12 weeks (Astra-Zeneca), but no earlier. My understanding is that they are following this guidance, pushing the second as far towards 11-12 weeks to maximise the number of people getting protection from a first jab. Pfizer has said that the effectiveness may reduce until the second jab is taken if delayed to 12 weeks, but this is a trade-off the Uk government has decided to take. There is some evidence that the efficacy may improve by delaying the second jab.
Basically, there are trade-offs but it is not reckless to delay the second jab.