This is not a Bulldog Drummond picture despite the title playing off Jack Buchanan and his previous association with the character. Here he plays the role of Test Pilot 'Bulldog' Bill Watson. His friend Derek Sinclair (Sebastian Shaw) is convinced that the new man in his love's life is collaborating with the Nazis by sabotaging an armaments plant.
Chorus girls Irene and Joan are discussing the war in their dressing room. Joan flicks through a copy of Picture Post with "Your Country Needs You" on the cover, and says she doesn't think she'd be cut out for war work and doesn't like being made to feel guilty about not volunteering. Irene says she has been thinking about it. As they leave by the stage door, a woman faints on the pavement in front of them. A newspaper seller says that the woman has just finished a 12 hour shift in a munitions factory and is exhausted, and that such long hours are necessary because of the shortage of workers.
In 1916 Jerusalem, German troops led by Von Schiller arrest French wine seller Paul Rouget for spying and hang him. His daughter Juliet goes into hiding dressed as a boy and starts spying on the Germans.
The film opens with shots of the London streets in late afternoon, as people begin their commute home. The narrator reminds the audience that these people are part of the greatest civilian army the world has ever known, and are going to join their respective service before London's "nightly visitor" arrives. Listening posts are stationed as far away as the coastline and the "white fingers" of searchlights touch the sky.
As the picture opens, a re-enacted phone call featuring reporter Cornelius Vanderbilt, Jr. in Germany, and narrator Edwin C. Hill in New York is depicted. Then a parade of people carrying torchlights in Berlin, where Jewish works and other political books are burned. Vanderbilt meets with Hill, and then flies out of the country. Hill talks with Vanderbilt about the problems in his country, then a re-enacted interview between Adolf Hitler and Vanderbilt. During a viewing of World War I battle footage, Hitler's home town, Leonidad, Austria, and his parents' graves are pictured. Vanderbilt goes to Vienna, to see Chancellor Dollfuss, and he films several Austrian Nazi riots during a parade. In a re-enactment, Vanderbilt's passport is stolen, and there are several shots of Nazis abusing Jews. In yet another re-enactment, Vanderbilt interviews Crown Prince Wilhelm, and more books are burned. Helen Keller talks to an interviewer about her books, which were burned by the Nazis. Then a conversation Vanderbilt, Kaiser Wilhelm II in Doorn, Holland, and Prince Louis Ferdinand had is re-enacted. Actual anti-Nazi speeches given by prominent Jews and some Gentiles are shown and the Nazis are shown trying to alter the Bible. In the final scene, Congressman Samuel Dickstein of New York and Hill give speeches directly to the audience, explaining the dangers of Nazism.
Dr. Karl Kassel (Paul Lukas) comes to America to rally support for the Nazi cause among German Americans. He instructs his audience at a German restaurant that the Führer has declared war on the evils of democracy and that, as Germans, they should carry out his wishes. Kurt Schneider (Francis Lederer), an unemployed malcontent, joins the cause and eventually becomes a spy for the group. A letter written by Schneider to a liaison in Scotland is intercepted by a British Military Intelligence officer (James Stephenson), leading to the ring's downfall.
At the start of the Second World War, musician George Hepplewhite (George Formby) gets on a boat thinking he is on his way to Blackpool, but arrives in Bergen, Norway instead, where he is mistaken for another ukulele player. He then meets the desk girl at the hotel, Mary Wilson (Phyllis Calvert), who is a British undercover agent and thinks he is one too. The duo manage to find and break a code that the Nazis are using to sink Allied shipping. A noted sequence was a dream where George had been given a truth drug by the Nazi conductor Mendez, in which he gives Hitler a right hook.
In 1940, the East Dudgeon lightship's seven-man crew are waiting for the arrival of another crew to relieve them of their duties so they can return home. While they are waiting, a momentary danger is encountered and dealt with: a drifting mine comes perilously close to the ship and the crew call for a minesweeper to destroy it.
The film opens with sisters Caroline (Mary Clare) and Edith Grant (Martita Hunt) preparing to shelter in their cellar following an air raid warning. When a man in uniform collapses outside their cottage, they bring him into their home and lay him down on their sofa. When he dies, they realise that the man is a German parachutist and, hearing the church bells tolling to warn of invasion, Caroline takes his revolver from him.
A group of schoolchildren from London are preparing for evacuation. After a medical examination, they meet at a railway station, uncertain of their destination. The train arrives and their journey to the countryside begins. Many of them have never seen the countryside before, and enjoy looking out of the carriage windows during the trip.
In the fictional country of Moronika, three munitions manufacturers—Messrs. Ixnay (Richard Fiske), Onay (Dick Curtis) and Amscray (Don Beddoe)—decide their country is in need of a change. They decide to implement a dictatorship, oust the king, and go about finding someone stupid enough to be a figurehead leader. Ixnay volunteers the three wallpaper hangers simultaneously working in his dining room—the Stooges.
A Royal Air Force (RAF) airman who dies during a mission has left a letter to be sent to his mother upon his death. The letter is delivered to his mother. As the letter is read out by his mother in the airman's room, she looks through his things and remembers him as a youth. The letter tells of his reasons for joining the air force and going to fight, knowing full well that he could die.
A successful American woman, Editor at The Smart World - Editorial, General Offices, Carol Cabbott (Joan Bennett) has just married a German, Eric Hoffman (Charles Lederer), a streamline marriage. They have a seven year old son, Ricky (Johnny Russell). They are to have a vacation to Germany to visit Erics father he didn't see for ten years, although everybody tells them to go to Germany is foolish. A friend, Dr. Hugo Gerhardt (Ludwig Stössel), originally german, asks them a favor: his brother, the famous philosopher Gerhardt has been arrested and put in a concentration camp, if they can bring him money and somehow help him.
Churchill's Island describes the military and civilian elements that were involved in the Battle of Britain. The Royal Air Force in an epic battle with the Luftwaffe, was able to wrest control of the skies, while the Royal Navy controlled the sea lanes around the embattled island. Other aspects of the struggle that are depicted included the British coastal defenses, the establishment of a mechanized cavalry, the role of merchant seamen and, after the Dunkirk evacuation, the re-building of a decimated British Army.