It takes its name indirectly from the flasks made for the mineral water produced at the nearby Hampstead Wells.
The Flask public house is located near the western end of the street and was built in 1767, although the current building is Victorian.
[1][2] An earlier Upper Flask Tavern was a meeting place of the Kit Kat Club of the early eighteenth century, located in nearby Heath Street.
[3] A number of buildings in the street are now Grade II listed, many dating from the Regency era of the nineteenth century or earlier.
A planned station of the Metropolitan Railway was due to be located at the eastern end of the street, but although authorised in the 1860s it was never constructed.