Green’s Dictionary of Slang

(orig. W.I.) a friend.

1973		Sun. Times Mag. 30 Sept. 32: Then I grew wise and started staying at a spar’s [friend’s] house.
1984		Smiley Culture ‘Cockney Translation’ 🎵 Say cockney have mates while we have spar.
1997		C. Newland Scholar 70: Shannon was already back from ’er rave, with Mikey an’ some of his spars.
2000		J.J. Connolly Layer Cake 33: I don’t suppose you would [feel sane], not after you’ve been covered with your spar’s blood and brains and that.