Brakes appear to be grabbing - Astra 2005?

The car was stood for a month in mostly wet Scottish weather. Upon driving it i can feel a definite "pulse" through the brake pedal. The disks are not warped and there is little or no vibration through the steering wheel. At walking pace the brakes (front) appear to brake then grab, then brake in rotation with the wheel - hence the pulse at high speeds. Pad lining is 8mm. Any ideas? Halfords say the brake pads need bedding in again after the disks have rusted, but i'm not so sure.