In 1943, Michel Hollard stole into a railway station in rural France and changed the course of the Second World War, sparing London from a 24-hour bombardment by V-1 "Doodlebug" missiles.
Some 61 years later, the French engineer's son, Vincent, spoke yesterday of his pride as dignitaries gathered at Waterloo Station to mark the naming of one of the Eurostar trains that link Britain and France after the war hero.
Denis MacShane, the minister for Europe, who attended the unveiling, said: "Michel Hollard's efforts doubtless saved many British lives and national treasures."
After the war, Hollard was decorated by the French and British and became known as "the man who saved London". But his espionage actions, which involved crossing about 100 times from France to Switzerland and establishing a network of railway informers, were overshadowed by the endeavours of the Gaullist Resistance until last year when campaigners called for a memorial.
Vincent Hollard, 74, who was himself decorated for his wartime activities as a teenager, said: "Because he was not formally part of the Resistance, my father's work has tended to be obscured.It is a fitting tribute that his memorial should be a link between France and Britain."
Hollard used his business manufacturing charcoal-powered vehicles to travel throughout wartime France. In the summer of 1943, one of his agents reported that a large number of unusual building sites had cropped up in Normandy.
Disguised first as a Protestant pastor and then as a labourer, Hollard obtained the locations of the sites and entered one of them, finding a concrete take-off strip. He then passed his information to British intelligence officers in the Swiss capital, Berne.
When another agent got hold of a masterplan showing a launch ramp and missile silo, British intelligence became convinced that V-1 attacks were imminent.
Final confirmation came when Hollard copied the dimensions of a V-1 stored in packing cases in the station goods shed in the Normandy village of Auffay.
In December 1943, using information provided by Hollard, the RAF began an intensive bombing campaign to destroy the V-1 operation. Historians calculated that without Hollard's efforts the V-1 bombardment would have been six times more severe than it was.
Despite being arrested in 1944 and tortured by the Gestapo, Hollard survived the war when the ship delivering him to a concentration camp was bombed and he escaped. He died in 1993, aged 97.
Vincent Hollard said: "We know that his information stopped between 2,500 and 5,000 missiles a week being launched. He didn't like to talk about what he did but I think he knew its importance."