Please answer one of the eternal mysteries of the Universe?

Probably, this is why. I can't be exact though.

"Coming into the last match of the 1988 season, against Ireland at Twickenham, England had lost 15 of their previous 23 matches in the Five Nations Championship. The Twickenham crowd had only seen one solitary England try in the previous two years and at half time against Ireland they were 0-3 down. During the second half the floodgates opened and England scored a remarkable six tries in a thumping 35-3 win. Three of the tries came in quick succession from Chris Oti, a black player making his Twickenham debut. A group from the Benedictine school Douai started to sing a rugby club favourite – the gospel hymn Swing Low, Sweet Chariot – in honour of their new hero, the whole crowd joined in. The England national rugby union team returned from the 2003 World Cup triumph in Australia on a plane dubbed 'Sweet Chariot'.

The song is still regularly sung at matches by supporters."

For further info check out the link below.

I don't know either but I think it's a bit of girly song to be singing. It cracks me up when they try to use it as a reply to the haka.

Same with Waltzing Matilda with the australians.... I've just never quite understood it.