The one of 1828 provided a sliding scale.  
They had existed since the Middle Ages, but only became a hot political issue after 1815.  The one of 1815 banned foreign imports until domestic prices had reached 80 shillings a quarter.  The one of 1828 provided a sliding scale.  A league against them was founded in 1839, and they were abolished in 1846.  FTP name these laws loathed by David Ricardo that regulated the price of grain.
They had existed since the Middle Ages, but only became a hot political issue after 1815.  
Corn Laws