I spoke too soon.
Today in the post we received all the paperwork for the car transfer and our cheque back in the post.
It appears (I hope) that the person dealing with our paperwork in Tours has grabbed the wrong end of the stick and has started running.
What the letter is saying is that we need to complete all the paperwork needed to import the car into France. As the car is already registered in France, this would mean exporting it to the UK, doing all the changes necessary to make it comply to UK standards and then register it. We would then have to export the car from the UK to France, undo all the the changes done so that it can be registered in France again.
This appears unnecessarily complicated and costly. I hope a polite letter will solve this, as we have now passed our 1 month limit for doing this transaction.