Considered the unofficial anthem of Britain, this song is actually music by Hubert Parry (around 1916) and words by poet William Blake (1808). The lyrics are commonly thought to mean Britain would be like heaven if Jesus visited. The anthem had been used to build troop morale back in the First World War. And British political parties of varying ideological stripes have also sang the lyrics at meetings and conferences since.
Another WWI song reviewed here: Paul McCartney, Pipes of Peace