It's not a true story. 'The Ipcress File' was created by the imagination of the author or screenwriter. It's purely fictional for entertainment purposes.
Well, the 'Odessa File True Story' is about a really intriguing plot. Basically, there's a search for truth regarding some Nazis who escaped after World War II. The Odessa in the title refers to an organization that helped these Nazis flee and hide. A person, often a journalist or someone in a similar role, starts to dig into this mystery. They face all sorts of threats and challenges as they try to expose what really happened and where these war criminals are. It's a story that combines history, mystery and a bit of adventure.