It is the traditional flag of Middlesex, the historic county that forms the central and north-west parts of Greater London.

[1] On Middlesex Day (16 May) in 2022, the Middlesex Flag became the first county flag to fly over 10 Downing Street, the official residence of the Prime Minister of the United Kingdom.

[citation needed] The flag is a banner of the arms of the former Middlesex County Council, abolished in 1965.

Whilst such banners of county arms are legally not generally available for public use, a similar design, with Anglo-Saxon Seaxes had been used traditionally as a local badge in Middlesex and neighbouring Essex for centuries.

The pantone colours for the flag are:[1]