breaking open a bike lock (advice please)

hi ef,

suddenly i cannot open the lock on my bike, it probably got rusty, it was in fact the second cheapest lock at halfords. i've tried swearing at it and kicking it, i also kicked my bike and then the rail it's locked to, but no luck. basically i'm going to have to break it open ... somehow.

the lock is a black u-lock. i thought maybe buy a hacksaw...but these are fairly expensive and it might not work.

any ideas?