This is from the IVA manual -
Note 4: Either of the following scenarios will also be
considered acceptable:
The rear fog lamp(s) may continue to operate until the
position lamps are switched off, and the rear fog
lamp(s) must then remain off until deliberately
switched on again or,
An audible warning, additional to the mandatory telltale
light, must be activated if the ignition is switched
off or the ignition key is withdrawn and the driver's
door is opened, whether the lamps in (RS4) are on or
off, whilst the rear fog lamp switch is in the "on"
position.
I've fitted one of these - REAR FOG LIGHT CONTROLLER for new IVA rules | Car Builder - Kit & Classic Car Parts Specialist