The song was written by Joe Strummer and Mick Jones. The title alludes to the BBC World Service's station identification: "This is London calling ...", which was used during World War II, often in broadcasts to occupied countries.
The lyrics reflect the concern felt by Strummer about world events with the reference to "a nuclear error" – the incident at Three Mile Island, which occurred earlier in 1979. Joe Strummer has said: "We felt that we were struggling about to slip down a slope or something, grasping with our fingernails. And there was no one there to help us."
The line "London is drowning / And I live by the river" comes from concerns that if the River Thames flooded, most of central London would drown, something that led to the construction of the Thames Barrier. Strummer's concern for police brutality is evident through the lines "We ain't got no swing / Except for the ring of that truncheon thing" as the Metropolitan Police at the time had a truncheon as standard issued equipment. Social criticism also features through references to the effects of casual drug taking: "We ain't got no high / Except for that one with the yellowy eyes".
The lyrics also reflect desperation of the band's situation in 1979 struggling with high debt, without management and arguing with their record label over whether the London Calling album should be a single or double album. The lines referring to "Now don't look to us / Phoney Beatlemania has bitten the dust" reflects the concerns of the band over its situation after the punk rock boom in England had ended in 1977.
The song fades out with a Morse code signal spelling S-O-S, reiterating the earlier urgent sense of emergency, and further alluding to drowning in the river.