A letter addressed to Theresa May was delivered to a rented flat three miles away in Islington.
Royal Mail bosses have apologised for the blunder after the letter was posted to 10 Danbury Street instead of 10 Downing Street.
Technology consultant Sam Bass, 24, said he showed the envelope to his housemates in disbelief when he came across the letter marked clearly for “Ms Theresa May, PM”.
He said: “I’m in rented accommodation, so we often get letters addressed to previous tenants. I decided to go through the post that had not been taken and was quite surprised to see one for Theresa May.
“I showed my housemates, but it would not have been for them. I live with a Marco and an Emily, neither of which look like Theresa.
“I can perhaps understand why the postal worker got the address mixed up, because the handwriting is quite poor and they look similar, but the recipient’s name is unmistakable.
“As far as I’m aware, the prime minister has never lived here.”
Mr Bass reposted the letter on Sunday night, adding: “I’m sure there’s probably nothing confidential inside, but it’s just as well it didn’t get delivered to somebody less honest.”
Sally Hopkins, a Royal Mail spokeswoman, said: “We would like to apologise for this delivery error. Every item of mail is important to us and staff are being reminded to check mail thoroughly before delivery.”
