I just tried that online booking website.
From the info there you still won't be invited until 6 months after your second jab, but you can book yourself after 5 months.
If you go on to (try and) book you will be told you are in a queue with a 5 minute wait, which seems an odd thing for a webpage form to say.
They must be rationing access so that the server doesn't get swamped with everyone trying at once and so crashing the server.
It doesn't matter how big it says the queue is, 100 waiting or 500 waiting it still says 5 minutes.
You will be asked for your 10-digit NHS number, (you can still carry on if you don't know it), then your date of birth to check that you are eligable.
You are then asked for your postcode and are given a choice of places to go and get your booster.
This is where I gave up for now.
My nearest offered was about 4 miles away, a pharmacy in the middle of a housing estate with a 1 mile walk down, and so back up, a steepish hill from the bus stop.
The next nearest was over 10 miles away, the others were even further and getting ridiculous.
OK, personally I could manage that hill, it wouldn't be pleasant if it's pissing down as usual. But many wouldn't be able to walk it comfortably/safely.
As usual it seems that they simply assume that everyone is fit as a fiddle, or has access to a car, or money to pay for a taxi.
I'll try again later and see if they offer the place where I had my first 2 jabs.
At 5 miles that's bit further but it's only a 100 meter, flat and level, walk from the bus stop.
It does make me wonder though if the booster programme take up problem is the same as it was at the start of the vaccinations last year.
Maybe the reason people aren't taking the boosters up as expected is because they are once again being offered appointments at ridiculous to get to places?