Coat of Arms of Middlesex County Council

Coats of arms were attributed by the mediaeval heralds to the Kingdoms of the Anglo-Saxon Heptarchy. That assigned to the Kingdom of the Middle and East Saxons depicted three "seaxes" or short notched swords on a red background. The seaxe was a weapon carried by Anglo-Saxon warriors, and the term "Saxon" may be derived from the word. These arms became associated with the two counties that approximated to the kingdom: Middlesex and Essex. County authorities, militia and volunteer regiments associated with both counties used the attributed arms.

In 1910, it was noted that the county councils of Essex and Middlesex and the Sheriff's Office of the County of London were all using the same arms. Middlesex County Council decided to apply for a formal grant of arms from the College of Arms, with the addition of an heraldic "difference" to the attributed arms. Colonel Otley Parry, a Justice of the Peace for Middlesex and author of a book on military badges, was asked to devise an addition to the shield. The chosen addition was a "Saxon Crown", derived from the portrait of King Athelstan on a silver penny of his reign, stated to be the earliest form of crown associated with any English sovereign. The grant of arms was made by letters patent dated 7 November 1910.

The undifferenced arms of the Kingdom were eventually granted to Essex County Council in 1932. Seaxes were also used in the insignia of many of the boroughs and urban districts in the county, while the Saxon crown came to be a common heraldic charge in English civic arms. On the creation of the Greater London Council in 1965 a Saxon crown was introduced in its coat of arms. Seaxes appear in the arms of several London borough councils and of Spelthorne Borough Council, whose area was in Middlesex.