Middlesex Day recalls the history of Middlesex County, which incorporated central London, and stretched out to Staines.
Middlesex was originally known as 'Middle Saxon' and was first recorded in 704 in a Saxon Charter and many within Spelthorne continue to identify with the county and flag today.
The distinctive design of the former county flag contains a gold crown and three short-notched seaxes on a red background.
The heritage of the county still lives on and imagery of the county, baring the crest and flags, can be found across the borough on local landmarks.
Russell Grant, president of Middlesex Heritage & Spelthorne Heritage, said "Spelthorne has a very special place at the heart of Middlesex' heritage. Spelthorne Borough Council bears the name of an ancient Middlesex Hundred: an administrative area dating way back to mid-Saxon times.
Middlesex Day celebrates 1320 years of our great County but please, not be confused with a Middlesex County Council, which lasted only 76 years and even then, ruled only two thirds of the geographical County. The two are not and have never been the same.
May 16th, was chosen as our County day in remembrance of the heroic Middlesex Regiment. On that day in May 1811 the Middlesex held back the might of Napoleon at the battle of Albuhera, Spain, where they earned the glorious nickname: 'The Diehards'.
The Middlesex' Great War regimental drum is forever under the guardianship of St Mary's Church, Staines, where it hangs with the County's colours in memory of the men of the Middlesex who made the ultimate sacrifice. All towns and villages in the Borough are tightly bound together under one richly historic identity - that of Middlesex. Not just for one day but always. May 16th is a time to celebrate, remember and recognise our very own County of Middlesex."