The pre-1801 Union Flag (of w:United Kingdom of Great Britain).
Made by Hoshie

Sodipodi flag collection (original file) Dead link as of: 4FEB2009
Colours: vexilla mundi Dead link as of: 12DEC2007 (Archived from 12MAR2007)
Proportions: Zscout370 and Madden
Hoshie