As a partially half-English person...my views are only partially valid.
We Welsh have the magnificent Hen Wlad Fy Nhadau, Scotland have Flowers of Scotland, a modern day folk Song written in the 1960s...The Irish are going to use an Ireland's Call, which is again recently written.All 3 of those are rousing songs.
.................GSTQ is not.....
Jerusalem is rousing, and is built on the great myth that Jesus visited Glastonbury (when Eavis farm still had cows?)...and if you forget the religious stuff...it fits the bill down to the ground.
but you English stick with GSTQ, you might have fallen asleep by the time you get on the pitch,....as that is the only chance that the injury-ridden Welsh have of getting through (that is assuming that we have beaten Fiji, which is also currently unlikely)