One is a basement flat in north London, and the other is among the most famous addresses in the country. And yet, somehow the mail destined for 10 Downing Street managed to find its way to 10 Danbury Street in Islington.
As you can imagine, it came as quite a surprise to technology consultant Sam Bass when he was involved in a case of mistaken identity with none other than the PM.
And while the postman responsible could be forgiven for confusing the scrawled Westminster address with the terraced townhouse in the north of the capital, the intended recipient "Ms Theresa May, PM" is distinctly legible. Whoops.
The letter, delivered by the Royal Mail from a north west Midlands address, was post-marked on November 19, but was only discovered this weekend.
Bass 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'.
He added: "And as far as I'm aware, the Prime Minister has never lived here."
Royal Mail spokeswoman Sally Hopkins 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."