1) Song from 18th century when we were engaged in the slave trade.
2) "Britain never ever shall be slaves" "none so blest as thee"
i.e A song bragging about how we're not the ones being enslaved, FROM WHEN WE WERE ENSLAVING PEOPLE.
A song from the slave days which gloats about slavery...
#GMB
Because being patriotic means believing that everything your country ever does or did is perfect.