The idea came to him when he was trapped in traffic on the Boulevard Peripherique, the perpetually choked mother of all ring roads. The news on the radio said that the city of Paris was considering doubling the size of the periph. Why not, thought Mr Lannaud, halve the size of the cars?
Six years later, his invention - a Mini-Minor cut in two - has been accepted by the Guinness Book of Records as the shortest "real" car in the world. With the help of a friend and a garage in his native Brittany, 69-year- old Mr Lannaud removed the back half of a Mini and re-attached the rear wheels, rear window and a part of the boot behind the front seats.
The result - the mini-Mini or Naudal, an approximate anagram of his name - is just over a yard long and can fit into half a Parisian parking space, with its front bumper to the curb. Unlike electric cars and other slow- moving, urban buggies, the Naudal is at home on the open road, and even on the motorway.
Mr Lannaud has the bouffant white hair and insistent, chest-prodding manner of a typecast Hollywood professor. But he is, in fact, a successful Breton clothes shop owner. He frequently pilots his invention at 90mph, suitcase on the roof, over the 300 miles from his small chateau in Brittany to Paris.
"Just look around you," he said, taking me for a nerve-jangling demonstration spin through the Parisian traffic. "You'll see few cars with more than one person in them. Most cars are unnecessarily big for what they're used for."
Looking around is not a good idea in the Naudal. In the front, and only, passenger seat, there is reassuringly plenty of space, even for a person of XXL size like me. If you glance behind, all you see is the road.
"And another thing," Mr Lannaud said. "This car drives itself." He took his hands off the wheel and turned to me with a grin. We were zooming down a narrow street, with parked cars on either side. A red light was approaching fast. Screech. "And the brakes work fine, too," Mr Lannaud announced.
He has already hawked his idea around a number of car companies, including Rover, successors to the makers of the Mini, but has attracted no more than polite praise.
If only the city of Paris can be persuaded to give his car an official blessing, Mr Lannaud is convinced that the Naudal's global and commercial future will be immense. "In the early days of motoring, Paris was the first city to abolish the external klaxon. All the other countries followed."
Mr Lannaud is pestering the Parisian authorities to give his two-seater the same status as motorcycles, which are allowed to park for free.
To force the issue, he has been parking his mini-Mini with its face to the pavement without feeding the parking meter. His intention is to generate a cause celebre by accumulating parking fines and fighting them through every court in the land.
Much to his chagrin, the Parisian traffic wardens find his vehicle so amusing that they have declined, so far, to give him a ticket.