You are required to carry a spare tyre.

You can be yellow stickered for not carrying a spare tyre.

In reality, you wont get yellow stickered for this alone, it will be dark tint, oil leaks, BOV's that vent to atmosphere, loose batterys, car too low, exhaust too loud, no cat converter and non-working headlights that will be the primary cause for a yellow. No spare tyre will simply be added to the list.

Clear as mud?