I think i need to book in much further in advance. Hard to get an appointment late enough. I will persevere though. This thread had prompted me to book in again.
I tend to book my next appointment while eating my biscuit(s) after my donation. That way I can have the day and time of my choosing as they're (almost) always empty. I really do suggest the permanent donation places as they're much faster and open later.
You can go after work at the West End donor centre (just by Oxford Circus), it's much nicer than a pop-up venue and they're very quick.