Had a warning light come on my Peugeot 207 saying air bag fault. ?

I wouldn't worry about it as the light has gone out. If it comes on again you might want to get the car plugged in to a code reader/ diagnostic machine. It should only cost about £30 at an independent garage.
Even if the light stays on, remember the airbag system is NOT a legal requirement, your car would not fail an MOT with the light on.
The car is perfectly safe and legal to drive, though admittedly slightly less safe to crash!!
I assume the bulb is still functioning, i.e. comes on with ignition then goes out after a few seconds.

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August 2009