England's Flag is the Cross of St George
The Union Flag (aka the Union Jack, though being very anal it's only a 'Jack" if flown from a ship) is just the three Saints flags of
England (St George),
http://www.flags.net/ENGL.htm
Scotland (St Andrew)
http://www.flags.net/SCOT.htm
and Ireland (St Patrick)
http://en.wikipedia.org/wiki/File:St_Patrick%27s_saltire.svg
overlaid on each other. Quite clever really.
The Welsh I'm afraid didn't get a look in, however no Welshman (or woman for that matter) worth their salt would accept that the Cross of St George as the Welsh flag !!
I actually regard the Welsh flag (Red Dragon on a green and white background)
http://www.flags.net/WALE.htm
to be one of the better UK flags.