Give carole nash a try, failing that try one of the online comparison sites to see what's out there.
Tips- Using a 'branded' lock and chain will bring down your quote as will stating you won't take pillion passengers.
garaging (or back garden) at night helps, as does doing less than 8K milage a year.
£140 a year isn't too bad for a first bike, is it fully comp? As usual it's all down to postcode.