Even a spare bulb kit without the Xenons was around £40. In the end, i took the one from my wifes Zafira so at least i had something to show the Gendarmes if i got stopped.I wonder if you could get away without taking replacement Xenons to France. After all the Owners Manual doesn't specify them as they should only be changed by an approved workshop.
I took spare headlamps (H7 non Xenon), and then a spare turn indicator and a spare brake lamp. The funny thing is, there is no actual law that requires the spare lamps. The kits and advice are actually only that - advice.I have taken a few cars with HID's to france and never taken a replacement head light bulb.
Unofficially, I do not hing the plod would expect a driver to carry these or replacement LED's with them.