I know you can book after 5 months and when I tried this I was given dates 6 months after my 2nd jab (so 1st Dec as 2nd jab was 1st June). Due to work diary I can't actually go until 8th Dec though so have booked that.
However there are walk in clinics near us which are primarily for flu jabs but are also offering boosters. Some friends went on Friday and got their jabs, but it was 1-2 weeks early i.e. before the 6 month mark.
Has the guidance/ eligibility changed? Shall I just go to a walk in clinic and hope to get it? I have lots of social things at the end of November and I'd prefer to have had the booster. I've already had my flub jab.