Captain Anson (John Mills) is the officer commanding a British RASC motor ambulance company. During the Western Desert Campaign of the Second World War when it is apparent that Tobruk is about to be besieged by the German Afrika Korps, Anson and most of his unit are ordered to evacuate to Alexandria. During the evacuation, Anson who is suffering from battle fatigue and alcoholism, MSM Tom Pugh (Harry Andrews), and two nurses, Diana Murdoch (Sylvia Syms) and Denise Norton (Diane Clare) become separated and in an Austin K2/Y ambulance, nicknamed 'Katy', decide to drive across the desert back to British lines.
As they depart they come across an Afrikaner South African officer, Captain van der Poel (Anthony Quayle), who carries a large pack, to which he seems very attached. After the South African shows Anson two bottles of gin in his backpack, van der Poel persuades Anson to let him join them in their drive to the safety of the British lines in Alexandria, Egypt.
Anson motivates himself by thinking of the ice cold lager he will order when they finally reach the safety of Alexandria – the 'Alex' of the title. En route, the group meets with various obstacles, including a minefield, a broken suspension spring (during its replacement, van der Poel's great strength saves the group when he supports "Katy" on his back when the jack collapses), and the dangerous terrain of the Qattara Depression.
Twice the group encounters motorised elements of the advancing Afrika Korps; in one encounter they are fired upon, and Norton is fatally wounded. Van der Poel, who claims to have learned German while working in South West Africa, is able to talk the Germans into allowing them to go on their way. The second time however, the Germans seem reluctant, until Van der Poel shows them the contents of his backpack.
This pack becomes the focus of suspicion. Pugh, already troubled by Van der Poel's lack of knowledge of the South African Army's tea-brewing technique, follows him when he heads off into the desert with his pack and a spade (supposedly to dig a latrine). Pugh thinks he sees an antenna. Later, at night, they decide to use the ambulance headlights to see what Van de Poel is really up to. He panics, blunders into some quicksand, and buries his pack, though not before Anson and Murdoch see that it contains a radio set. They drag him to safety. While he recovers, they realise he is probably a German spy but decide not to confront him about this. During the final leg of the journey Katy must be hand-cranked in reverse up an escarpment, and Van der Poel's strength is again crucial to achieving this.
When they reach Alexandria they make their way to a bar and Anson orders a cold beer, which he consumes with relish. But before they have drunk their first round, a Corps of Military Police officer arrives to arrest Van der Poel. Anson, who had prearranged this at a checkpoint as they entered the city, orders him to wait. Having become friends with Van der Poel and indebted to him for saving the group's lives, Anson tells him that if he gives his real name, he will be treated as a prisoner of war, rather than as a spy (which would mean execution by firing squad). Van der Poel admits to being Hauptmann Otto Lutz, an engineering officer with the 21st Panzer Division. Pugh notices that Lutz is still wearing fake South African dog tags and rips them off before the police see them. Lutz, after saying his farewells and concluding that they were "all against the desert, the greater enemy", is driven away, with a new respect for the British.
The film was based on a series of articles written for the Saturday Evening Post published in book form in 1957. The script made a number of key changes from the novel.
The producers had intended to shoot the location work for Ice Cold in Alex in Egypt, but the producers had to switch to Libya because of the Suez conflict. Sylvia Syms (Sister Murdoch) said in a 2011 interview about the film that conditions during the desert shoot were so difficult it felt like they were actually in the situation the film portrays. She said: "You may find this hard to believe, but there was very little acting. It was horrible. We became those people ... we were those people". She said that today people would probably call it method acting, but added: 'We didn't know what Method Acting was, we just called it 'getting on with it'."
Syms said that during the scene where the ambulance rolls backwards down the hill narrowly avoiding her, the actors assumed there would be a hawser to stop the vehicle if anything went wrong, but there was not. The actress said she was "pretty sure" Mills, Quayle and Andrews angrily upbraided director J Lee Thompson for this risky approach. She added: "He liked to push actors a bit".
The quicksand sequence was filmed in an ice cold artificial bog in an English studio (some scenes were shot at Elstree) and was "very tough" on Quayle and Mills. Syms said the producers got a good deal out of her for "£30 a week", adding: "But I made a lot more when they turned it into an advert for Carlsberg". She said there are "no false heroics in it" and that she had been told by desert war veterans it is a good picture of soldiers in that theatre of war, adding: "I am proud of it".
The film won multiple awards:Winner FIPRESCI Award Berlin International Film Festival
Nominated Golden Bear Berlin International Film Festival
The final scene, in which Mills' character finally gets his glass of lager, was reportedly filmed some weeks after the rest of the film, at Elstree. Real lager had to be used to "look right", and Mills had to drink numerous glasses full until the shots were finished, and was "a little 'heady'" by the end.
Sylvia Syms has said that the Danish beer Carlsberg was chosen because they could never have been seen to be drinking a German lager: since the United Kingdom and Germany are at war during the film, no German lager would have been available in British-occupied Alexandria owing to the lack of trade between hostile powers at the time when the film is set. The beer referred to in the original novel is Rheingold, which, although American, has a German name.
Scenes from the film were used in a late-1980s television advertising campaign for the German Holsten Pils lager. Each advertisement mixed original footage from a different old film (another example was The Great Escape (1963)) with new humorous material starring British comedian Griff Rhys Jones and finishing with the slogan: "A Holsten Pils Production". In retaliation, rival Carlsberg simply lifted the segment in which Mills contemplates the freshly poured lager in the clearly Carlsberg-branded glass, before downing it in one go and declaring, "Worth waiting for!" This was followed by a variation in the usual Carlsberg tagline: "Still probably the best lager in the world."
As Quayle is driven away as a prisoner-of-war at the end of the film, several post-war Land Rovers can be seen parked in the background. The Afrika Korps are shown variously equipped with American M3 half-tracks and an American self-propelled gun.
"Katy," the Austin K2 ambulance used in the film, was specially converted to 4-wheel drive, apparently for greater mobility during desert filming (the transfer case, front differential and front propeller shaft are visible in some shots). Genuine K2s were not so fitted. Harry Andrews also claims, "Katy weighs two tons!", whereas the actual weight of the K2 exceeded three tons.
In a break with previous films by Associated British Pictures, the producer and editor used a minimum of incidental music. Leighton Lucas wrote a stirring military march called "The Road to Alex", which was the main theme, and a "Romance".