Lyric discussion by Ummm... 

Oh, Jeez, people, this is about the most sarcastic song I've ever heard, right up with "Sultans of Swing".

Look, it's not straightforward at all. Let me break it down for you:

"In Penny Lane there is a barber showing photographs Of ev’ry head he’s had the pleasure to know."

He keeps a set of photos of everyone famous he's met, like an autograph book. Not too out there, but still strange behavior.

"And all the people that come and go Stop and say ‘Hello’."

The ordinary people of Penny Lane/Liverpool want to be near greatness, so they participate in the oddity, and stop in to look at the photos of people they'll never be.

On the corner is a banker with a motorcar, The little children laugh at him behind his back."

A rich banker (the motorcar shows he's rich) has lots of illegitimate children, their presence is mocking him (probably because he has to pay off their mothers)

"And the banker never wears a mac In the pouring rain - very strange."

Mack = raincoat = rubber = condom. Even though it's likely to get him ANOTHER illegitimate child (bastard), he continues to have sex without rubbers (because he's arrogant or likes the feeling better, whichever)

"Penny Lane is in my ears and in my eyes, There beneath the blue suburban skies I sitt, and meanwhile back"

He's (Paul) sitting observing and listening and ferreting out what is driving the people he sees - what's beneath the surface of their daily lives

"In Penny Lane there is a fireman with an hourglass And in his pocket is a portrait of the Queen. He likes to keep his fire engine clean, It’s a clean machine."

A man who keeps punctuality as a goal. Very indicative of the British Condition, subverting all of one's desires to an admiration and striving for a goal that one can keep, instead. He keeps a portrait of the Queen, another person he'll never reach or touch, but his perversion is that the Queen - a 'handsome' woman - is his masturbatory fantasy, and, like clockwork - punctually - he masturbates (keeps the fire engine clean) often - it is, after all, a clean machine, worthy of the Queen.

"Penny Lane is in my ears and in my eyes, A four of fish and finger pies In summer meanwhile back"

In the summer, when things are warm and free-er, boys finger women in the streets after dark...

"Behind the shelter in the middle of the roundabout The pretty nurse is selling poppies from a tray."

She's selling medical morphine and other narcotics to supplement her income. Nothing to do with war remembrance; it's a juxtaposition of the pretty nurse trafficking in stolen narcotics.

"And though she feels as if she’s in a play She is anyway."

Her actions are surreal to her, feeling justified because it's all unreal; but all the world's a stage, and she's a player doing it for Paul's benefit (his observation).

"In Penny Lane, the barber shaves another customer, We see the banker sitting waiting for a trim"

The Banker is waiting to see a mistress, and using the barber as a reason for being out of the office.

"And then the fireman rushes in From the pouring rain - very strange."

The fireman is afraid of women - the pouring rain symbolizes (as above) the potential for fathering children - and he rushes indoors (would rather masturbate because women terrify him).

Now, children, THAT's what the song is about.

typically life then what we all fear is condendensed into one song one street

Or...to anyone who's ever been to the UK or knows McCartney's background, there's a friendly barber with pictures of haircuts on his wall, and locals stop for a chat. And there's a bank manager who drives a nice car, who pops in for a haircut. And the portrait of a queen is either on some cash in the fireman's pocket or a photo of his wife. And the nurse is selling poppies because it's close to Remembrance Day, and that's what happens in the UK.
'Finger pie' though. Yeah.

@Ummm... I think divebiker got it right, it‘s not that dirty, the finger pie reference is some dirt for the guys back home, as Paul explained it some years ago.

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