I know this is an old thread but just a quick coda. The verse:

We have many goods for export, Christian ethics and old port
But our greatest boast is that the Anglo-Saxon is a sport
On the playing fields of Eton we still do thrilling things
But don't think we're ever beaten, oh the captains and the kings
But don't think we're ever beaten, oh the captains and the kings

Is a variation Ive heard on Phil Chevron's early 80s version of the song, before he joined The Pogues, I think.

It's a nice addition and reflects the public school influence still so prevalent in the British ruling class.