Just a quick update on this.
Had my original appointment on Tuesday, the 17th of September. Sat at the appointment for nearly 3 hours before giving up during this system outage. Re-booked and paid (again) for an appointment on Monday, the 23rd of September.
Yesterday, all went smooth and I was in and out in about 30 minutes time. (London Premium Center)
**Key info here**
I just got off the phone with the free number I was given (0330 123 1199) to request a refund on the first appointment. Surprisingly, they refunded me in full for BOTH appointments! Very happy with that result.
Best of all, my visa approval email came in this morning bright and early at 10am.
Good luck to anyone else that was affected by this.