In case you haven't heard (and I didn't know), just picked this up
from the Rover 75 and MG ZT Owners Club forum. A later post suggest
that it applies in most other European countries as well (except UK -
yet):

"A new law (applicable now) means any person planning to drive in
France must carry a reflective jacket from now on. In an emergency,
the jacket must be easily accessible by the driver and must be put on
before leaving the car, day or night, regardless of visibility. As of
1 October 2008, any person found not complying will face a 135 euro
fine (90 euro if paid early).

I've not seen any reference requiring passengers to have a jacket, so
it looks like the driver only (at this stage). For me, the new news
was that the jacket has to be accessible from inside the car. I was
relying on mine being inside the tailgate along with the warning
triangle. That's not good enough! From October 2008, cyclists will
need high viz jackets outside built-up areas too - and we think the UK
is bad for Health and Safety!

I've found a company that sells suitable jackets for £1.69 each (plus
a few pence for P&P).
http://www.vizwear.com/detail.php?p=1&c=0.1&subc=1 I've no connection
with the company, but plenty of connection with trying to make my
money go as far as it can!"

PLUS

"Yep,confirmed 135 euros,i work over here in France and we were told
to get one in our cars ASAP,so we put it in the boot as is the norm we
thought,wrong,easily accesible is the wording and as such in the car
it is,most of le frogs seem to be sticking it over the passenger seat
at the moment and the Gendarmes are having a field day with Brit
tourists down here (Toulouse area),so invest in the kit and stick it
in the car not in the boot.
Oh,and it's from July 1st according to our bosses!!!"