Some good info on here thanks, though fear I might have found it too late 😞.
After a recent service, I had a sporadic 'Brake Servo: restricted. You can continue driving. Please contact workshop' message. I intended to call and discuss with the dealer, but it disappeared and I saw no obvious change to braking.
This message then recently returned and I noticed a light clicking/grinding sound when applying the break at very low speeds (crawling in traffic/slowing for expected traffic light changes/parking), before I've had chance to book in for inspection following it's return, it's now switched over to 'Brakes: fault. Safely stop vehicle' and the red warning, there are no other lights, no ABS light etc.
I'm calling the dealership shortly, but with what I've seen in the thread I'm fearful that I've progressed through the 'You can continue driving......' -> '......therefore knackering the ABS' trap 😞
Particularly galling, as I made the switch to an Audi on reputation (and that I've always wanted one) but also necessity, when my Ford Focus trashed it's engine due to a 'known fault' with the Ecoboost cooling system and temperature reporting... Effectively wrecking it's own head gasket/engine one fateful ten minute drive. At 20k miles and feeling still almost brand new, I wasn't expecting a fault of the likely costs if my fears are correct.