ha, right. thought it said "MB"... i dunno, os files incorrectly labeled in that window? try running disk first aid perhaps, or reboot. also... does it look right when you consider the files you actually have on your mac?
Thanks, didn't actually notice that you could take further actions there. Turns out to be backups right enough...bizarrely there are about 10 different backups all 18gb in size Anyway thanks guys