I don't know the hymn, even though we used Songs of Praise at school. However, these look like the words you are after:

WHAT HEROES THOU HAST BRED

What heroes thou hast bred,
O England, my country!
I see the mighty dead
    Pass in line,
Each with undaunted heart
Playing his gallant part,
Making thee what thou art,
    Mother of mine!

Then let me take my place
O England, my country!
Amid the gallant race
    That is thine,
Ready to hear thy call,
Ready to give thee all,
Ready, whate'er befall,
    Mother of mine!