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Yes, you should do that while filling the form online.1. form filled out online and should i pay the NHS surcharge beforehand (im thinking yes)
Appointment are based on availability, I cannot answer exact but you will see date and places which are available. As far as I know croydon is nearest in London.2. how close to the day you filled out the form were you able to get an appointment
I think it is pretty easy and relaxing however, you will be a bit nervous (I was). I had booked the first slot it was 8:45am. I suggest you not to book super early as I was almost late due to road works and diversion (maybe book 9 or 10). Arrive early atleast 15-20 mins. As far as I remember once you enter they will check everything like in airport then you go up to the main area you will submit your application then they will ask you to wait. They will give you a Token Number and you can monitor status in a Monitor so you just have to wait. Later on they will call you your Token Number and you go get your BRP done (they will take photo, fingerprint), again you'll be waiting and this is when they will access your application and you will be waiting for your result. You can see your Token Number in monitor. And once it is your number you go and they will tell you about your result.3. what exactly happened on the day of the appointment