The journey from Narbonne to Paris was by Corail rather than by TGV. The reason for this was simply that the TGV trains don't take bicycles, except if they can be handled as luggage, i.e., folded and bagged. Folding a mountain bike and all its paniers and bits and pieces wasn't an option. Hence the long journey was that much slower, but it was probably better than a coach.
When I got to Paris, I had to get from the Gare d'Austerlitz to the Gare du Nord. This meant cycling through dense rush-hour traffic in pelting rain - not an experience to be recommended, because though cyclists are entitled to use bus-lanes, bus-drivers don't seem willing to share. I spent a long time cycling on pavements to avoid being mown down by the buses.
To take a Eurostar train with a bicycle, you have to book the bike on the train in advance as unaccompanied luggage. I did this in London when I obtained my ticket, but you can't book this at the normal ticket-offices or at the Raileurope office. Once you have your ticket to travel (and not before) you have to go to the EuroDespatch Centre in person at St Pancras International. Charges are £20 one way and you have to quote your Eurostar reference or show your ticket.
In this way, I obtained a label with a bar code that has to be attached to the bike for the journey. I showed this to the people in the Sernam office in the Gare du Nord. There was much sucking of teeth and discouraging Gallic sound-effects. The chap told me firstly that I couldn't expect my bike to travel on the same Eurostar train as myself and that I may have to wait in St Pancras for some time. He then informed me that I would have to strip the bike of everything that was not physically part of the machine and securely attached. This meant taking off all the panniers, saddle-bag, frame-bag, lights, lock, bottle and so on and then carrying all this back to the Eurostar check-in, which was not easy given the fact that the Sernam office is at the far end of the Gare du Nord and there are no trolleys down there.
I staggered to the check-in with my arms full of all this stuff and that was where the fun started. The check-in staff didn't like all the hardware I had in my hands - tool-kit, pump, light, bike-lock, bottle - which set the alarm-bells ringing when I put it all through the X-ray machine. They spent a good half-hour rushing around, throwing up their arms and vainly trying to decide if my tool-kit was dangerous or if my pump represented a hazard. There was even a suggestion that I would have to surrender all this stuff if I wished to board the train. Eventually simple common sense prevailed when a member of staff, himself a cyclist, simply pronounced my stuff harmless. The excitement died down like milk going off the boil and I was waved through.
When the Eurostar train got to St Pancras, I spotted my bike being transported on a trolley to the EuroDespatch offices. I stopped the driver of the trolley and he agreed to give me my bike if I could prove it was mine. Since no-one had given me any documents, I couldn't. In the end, I remembered that my name was written on the label attached to the bike and told him to look for it. He found it and when I demonstrated my identity, he reluctantly let me take the bike.
I cycled off down the now empty platform and was told to get off my bike by an official. I ignored him.
I arrived home at about 11pm, having left Narbonne at around 8.30 am London time. I would far rather have done another fifty miles or so on my bike.