Which Beatles song was inspired by an advertising jingle?

 It’s a throwaway, a piece of garbage...from a Kellogg’s cereal commercial. I always had the TV on very low in the background when I was writing and it came over ...{in this} song. 

During his Weybridge years, John Lennon was a British version of Benjamin Braddock in The Graduate (1967). Though extraordinarily privileged in material terms he felt alienated: a rich, successful young man angry at the suburban world he found himself in. This anger was largely expressed through petty acts of passive aggression against those surrounding him.  

In the conventional Beatles narrative, John Lennon was the wild man, with an artistic bent and a taste for the avant garde.  Paul, in contrast, was the son-in-law choice: cute, sensible and with the common touch. 

In reality, the roles were reversed. McCartney spent his Beatle downtime careering around  Swinging London in his Mini Cooper, the pop world's Toad of Toad Hall. He was a fixture of the hip clubs, fashionable parties and talked-about plays and art exhibitions. 

Meanwhile, John stayed in the Surrey suburbs. There he would mope around his mansion in his dressing gown, being surly to all and sundry. He did not (yet) alleviate his boredom by having an affair with an older married woman. His unhappiness manifested itself in booze, pills and epic self-absorption. This shut out Cynthia and Julian. It was not a happy home.

On the attack

GOOD MORNING GOOD MORNING channeled this inner rage into the angriest song on Sergeant Pepper. The immediate inspiration was the TV advert Lennon cites above, and he also seems to have been infuriated by a long forgotten British sitcom, Meet the Wife. 

A concealed motivation was to counter the optimism and sunny outlook of  McCartney's earlier GOOD DAY SUNSHINE. As Macdonald suggests, the 'splenetic gusto with which he lays all about him' was productive creatively. 

Later Lennon would dismiss the song as  'a throwaway piece of garbage ', in keeping with his dubious theory that Sergeant Pepper was essentially  'a bunch of Paul's songs'.  Yet  GOOD MORNING GOOD MORNING clearly shows his artistic intent. has a tremendous energy that is picked up in the track that follows SERGEANT PEPPER (REPRISE). 

If McCartney recognised the sonic ambush, he did not show it. His 'coruscating pseudo-Indian guitar solo' perfectly the matches the mood of the song, as does the pulsating brass score.

Further evidence of Lennon's dyspeptic mindset is found in the fadeout of apparently random farmyard noises. They form a sequence in which each successive animal has the potential to eat its predecessor. 

Not the image Kellog had in mind, though perhaps at one with some of the more disturbing theories of the cereal company's founder.

The Beatles - Teaching Materials