Robin Aitken of TVMM and Spring Grove MM has been along to the Kingston Local History Room & Archives and presents the evidence for Morris dancing in 1507.
Robin’s Page gives a number of useful and interesting links showing that the evidence has been known since 1792.
Included are these three photographs:

Spring Grove MM
Robin’s Page
Kingston Local History

Early Morris
The English Folk Dance and Song Society have a Morris Dancing Bibliography for the serious student.
Rose Moresk have a site dedicated to Early Morris, while
The Lion’s Part have more about May Games.
The Morris Ring has references for dancing before 1660
 

EFDSS
Rose Moresk
The Lion’s Part
The Morris Ring

The Betley Window
St. Alban’s MM have a page about the Betley Window (which is in the V&A) and an article from The Antiquary of 1912.
Mike Heaney has more details and European comaprisons. 

Betley Window
Mike Heaney

Updated Sunday 6th May 2007