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The Sheffield Royal Infirmary, site of the hospital scene.
Young Sheffield residents Ruth Beckett (Karen Meagher) and Jimmy Kemp (Reece Dinsdale) are planning to marry due to her unplanned pregnancy. Meanwhile, as tensions between the US and the Soviet Union over Iran escalate, the Home Office directs Sheffield City Council to assemble an emergency operations team, which establishes itself in a makeshift bomb shelter in the basement of the town hall. After the ignored US ultimatum to the Soviets results in a brief tactical nuclear skirmish, Britain is gripped by fear, with looting and rioting erupting. "Known subversives" (including peace activists and some trade unionists) are arrested and interned under the Emergency Powers Act.




Curbar Edge, Peak District, where the scenes set six weeks after the attack take place.
At 8:30Â a.m. GMT (3:30 in Washington, suggesting the Soviets fire first) on 26 May, the town hall office transmitter signals Attack Warning Red, and Sheffield's air raid sirens sound. Panic breaks out in the city and the Sheffield operations staff man their desks. At 8:35Â a.m. a single nuclear warhead air bursts high over the North Sea, producing an electromagnetic pulse which damages or destroys communications and most electrical systems throughout the UK and northwestern Europe. Two minutes later the first missile salvos hit NATO targets, including nearby RAF Finningley 18 miles (29Â km) from Sheffield. Although the city is not yet heavily damaged, the mushroom cloud from Finningley is clearly visible and chaos reigns in the streets, with Jimmy last seen running from his stalled truck in an attempt to reach Ruth. Sheffield is soon hit by a one megaton warhead launched at the Tinsley Viaduct. A title card states that strategic targets, including steel and chemical factories in the Midlands, are the primary targets, with two-thirds of all UK homes destroyed and immediate deaths ranging between 17 and 30 million. By the time the exchange is over, the resulting East-West exchange amounts to 3,000 megatons. About 210 megatons fall on the UK.
Sheffield Town Hall collapses in the attack and traps the city's emergency operations team in their shelter underneath it. From there the trapped team over the next several days attempts to coordinate the city's chaotic emergency and relief efforts through their few remaining short wave radios. Within hours, nuclear fallout from a ground burst at Crewe descends upon Sheffield on a northwesterly wind, with the badly burned Mrs Kemp soon succumbing to radiation sickness and severe burns due to being caught by the Tilsley Viaduct explosion. His three children dead or missing and his wife dying, Mr Kemp sets out on a desperate search for food and water, eventually dying himself. The dangers of fallout prevent the remaining functioning civil authorities from fighting fires or rescuing those trapped under debris. Ruth leaves her (still living) parents in their basement and after walking through the devastated city eventually makes her way to the Sheffield Royal Infirmary, where there is no electricity, no running water, and no sanitation, with drugs and medical supplies having long since run out. While she is absent, looters kill her parents but are subsequently executed for their deed.
A month after the attack, soldiers finally dig through to the town hall basement only to find the emergency staff all dead from suffocation. Burying the dead is a waste of manpower and burning them is a waste of fuel, and this leads to an epidemic of communicable diseases such as cholera and typhoid. The government authorises the use of capital punishment and convenes special courts to sentence and execute the new class of criminals. As money no longer has any value, the only viable currency is food, given as a reward for work or withheld as punishment. The millions of tons of soot, smoke and dust now in the upper atmosphere soon leads to nuclear winter. As the narrator intones, "it starts to get dark, it starts to get cold". Ruth is later seen working on a farm in Buxton, having defied official advice by fleeing the city and eventually giving birth to a daughter in a farm out-building.
A year after the war, sunlight begins to return but food production remains poor due to the lack of proper equipment, fertilisers, and fuel. Damage to the ozone layer also means this sunlight is heavy with ultraviolet radiation, with cataracts and cancer becoming more common.
Ten years later Britain's population has fallen to medieval levels of about 4 to 11 million people. The government manages to retain some semblance of contact with this remainder through its radio broadcasts. Survivors work the fields using primitive hand-held farming tools. Few children have been born or raised since the attack. They speak broken English due to the marginal, barely functioning education system and the breakdown of family life due to the war and its aftermath. Prematurely aged and blind with cataracts, Ruth collapses in a field and soon dies, survived by her 10-year-old daughter Jane (Victoria O'Keefe). By this time, the country is beginning to recoverâor at least function at the most basic levelâwith resumption of coal mining, limited electricity production, and some steam powered mechanisation derived from 19th century technology. Yet the population continues to live in near-barbaric squalor among the ruins and barely tenable subsistence farming.
Three years after Ruth's death, Jane and two boys are caught stealing food. One boy is shot in the ensuing confusion. Jane wrestles for the food with the other boy and they have (what the script describes as) "crude intercourse".[3] Months later, Jane finds a makeshift hospital and gives birth. The film ends just as she is about to scream in horror as she looks upon her stillborn baby.

Question: How many megatons fall on the UK?
Answer: 210 megatons