The one thing that has prevented this plan from being put into operation is that selling the gold on the black market in Britain would be too risky and Holland is at a loss as to how to smuggle it abroad.
One evening a new lodger — artist Alfred Pendlebury (Stanley Holloway) — arrives at the boarding house where Holland lives in Lavender Hill. Pendlebury owns a foundry that makes presents and souvenirs that are sold in many resorts, including foreign ones. Noticing how similar the foundry is to the place where the gold is made into ingots, Holland decides that the ideal way of smuggling the gold out of the country would be as "Eiffel Tower paperweights" for Paris, and puts this hypothetically to his new friend: "By Jove, Holland, it's a good job we're both honest men.", "It is indeed, Pendlebury."
When Holland suddenly finds that he is about to be transferred to another department at the bank, he and Pendlebury quickly move into action. They soon recruit two petty crooks, Lackery Wood (Sidney James) and Shorty Fisher (Alfie Bass) to help them carry out the robbery.
The plan is simple but clever and successful. Wood and Fisher carry out the hijack of the bullion van and switch the gold to Pendlebury's works van. Holland, who is supposedly assaulted and almost drowned in the robbery, becomes the hero of the hour. The police find themselves running around in circles, unable to track down the "master criminal" who is in fact right under their noses giving them false statements and misleading clues.
As in all great comic adventures, the plan goes horribly wrong through a (simple) misunderstanding with the (French) lady at the Eiffel Tower souvenir kiosk. Pendlebury and Holland (who have adopted the more macho names of "Al" and "Dutch") arrive to retrieve their disguised bullion only to find that six of the towers have been sold as souvenirs to a party of British schoolgirls!
A wild chase back to the channel ferry follows but all sorts of hold-ups, including problems with the customs men, prevent them from getting to the ship and the girls in time.
If just one of those towers is found to be gold then the game is up. Pendelbury and Holland therefore track down the schoolgirls and, in exchange for a similar tower and some money, recover most of the loot. One girl however refuses to return hers since she intends to give it to a friend who is a policeman.
The girl delivers the souvenir to the officer who is attending an exhibition of police history and methods at Hendon Police College. Also there is a police Inspector who is investigating the robbery and who checked up on Pendlebury's foundry and was told that many souvenirs bought in foreign places are actually made in England. A sudden thought occurs to him and he orders the souvenir to be tested. At that moment Pendlebury snatches it and he and Holland make their escape in a police car.
An increasingly confusing pursuit then takes place through London, with Holland using the radio in the police car to give false descriptions of the vehicle in which the "crooks" are in. Eventually, though, an officer succeeds in getting into their car and arresting Pendlebury.
Holland escapes to Rio de Janeiro where he adopts a lifestyle to which he is "unaccustomed" and becomes a pillar of the community. A year later he is telling his story to a British visitor before they both leave the restaurant handcuffed to one another, Holland having been found, arrested and due for extradition.
It is not made clear what happens to Wood and Fisher.
Explaining that they do not care to travel abroad, Wood and Fisher both trust Holland and Pendlebury enough to let them go to France without them, recover the gold, sell it and return with their fair share of the proceeds. Some might view this as "honour among thieves' or traditional British working class deference to middle class leadership, though an article in Empire magazine reportedly interprets it more politically as a metaphor for the faith put into Clement Attlee's post-war Labour government by the voters who were then, in the view of the article's author, "betrayed by their implicitly trusted betters" (note, however, that there is in fact no indication in the film that Holland and Pendlebury have the intention of betraying their confederates).
The scene where Holland and Pendlebury run down the Eiffel Tower steps and become increasingly dizzy and erratic, as does the camera work, presages James Stewart's condition in Alfred Hitchcock's Vertigo, made seven years later.
Audrey Hepburn makes an early film appearance in a small role as Chiquita near the start of the film. Reportedly, she was supposed to have had a major part in the film, but other commitments prevented this, so Guinness lobbied for her to be given a walk-on part. Playing an apparent consort of Holland's, she is given some money by Holland (a "birthday present") and says "How sweet of you!" before departing. This was the first film featuring Hepburn to be given major distribution in the United States (most of her other early roles were in movies that were only distributed in Great Britain or Europe).
Robert Shaw, later famous for his roles in such films as Jaws and From Russia With Love, makes his film debut in a wordless role as a chemist in the police exhibition sequence. He reportedly had several lines of dialogue that were removed from the final cut.
British 1960s children's television icon Valerie Singleton also had an uncredited part in the film. Given that she would have been 13 years old, she was probably one of the schoolgirls in Paris.
Guinness was nominated for the award of Best Actor in a Leading Role.
The film also won the BAFTA Award for Best British Film.