The whole thing started in Ruislip where I live so there's a lot of them round here.
Apparently they produced the first four for Valentines day, so this picture I took on 26 February must have been one of that earliest batch:
View attachment 48883
Then they produced some dozens of spring and Easter-themed toppers during March and April, and the whole thing took off on social media, then old-school media and the craze spread across the nation. So I'm told.
By June there was a book:
https://www.amazon.co.uk/Lockdown-Letterboxes-British-graffiti-knitters/dp/B095N4WY71
And now there's a 2022 calendar.
Oxo