Date: We know that it's in color and that he saw it before 2000.
Country of origin: Don't know. Could be the US, UK...
Genre: He said it was exciting, so action, crime maybe thriller.
It's set somewhere between 1945 and 1980, in England.
It's centered around a secret neo-nazi group. They have a flag that has a swastika on it but it's not the same flag used by the Third Reich.
This group plans to poison the water supply of every major town in England at the same time in order to take over the country.
They don't succeed.
It's not Dick Barton: Special Agent (1948) or The Heroes of Telemark (1965).