I am in process of moving to France from Switzerland, so needed to get french number plates in order to get the car import stuff completed. Since the import process takes a bit of time, so wanted to get the "provisional" number plates in order to cancel my swiss number plate (and not to pay the road tax + insurance for 2012). I bought my car from Switzerland about 1 1/2 years ago.
For regular import, one needs following documents:
1. technical control from a designated garage
2. conformity certificate from manufacturer of the car
3. import certificate from tax authorities in France
4. proof of residence (EDF bill, telephone bill, house insurance etc)
5. proof of buying the car (original receipt) + car documents
For the provisional plate one only needs the following documents:
1. proof of buying the car + car documents
2. proof of residence
The provisional plates could be obtained by visiting the regional "sous prefecture" (which was Mulhouse in my case). The service is pretty fast e.g. less than an hour including waiting time.
After getting the provisional numer for car, I visited speedy in St Louis and car plates were ready in an hour, cost = 20 EURO (remember to download 25% discount coupon from speedy.fr website).
Also when visiting the authorities, remember to ask for a "provisional" number since it is not clear to them, so insist on asking for provisional certificate if the reception guys ask you for detailed documents etc.
Now, I will do rest of the process but I hope that should be easier now. I have 30 days (+30 days extension) to do the rest.
Please message me if you would need any specific information. I am not sure if process to get provisional plates is same for UK imported cars.