Robin Aitken of TVMM and Spring Grove MM went along to the Kingston Local History Room & Archives and presents the evidence for Morris dancing in 1507 and after.
Included are these three photographs:

Spring Grove MM
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 31st October 2010