An old, mad, blind, despised, and dying king,—
Princes, the dregs of their dull race, who flow
Through public scorn,—mud from a muddy spring,—
Rulers who neither see, nor feel, nor know,
But leech-like to their fainting country cling,
Till they drop, blind in blood, without a blow,—
A people starved and stabbed in the untilled field,—
An army, which liberticide and prey
Makes as a two-edged sword to all who wield
Golden and sanguine laws which tempt and slay;
Religion Christless, Godless—a book sealed;
A Senate,—Time's worst statute unrepealed,—
Are graves, from which a glorious Phantom may
Burst, to illumine our tempestous day.
Shelley is saying that Parliament provides a corrupt form of leadership.  Their immense power prohibits challenge; hence the ‘statute un-repealed’.  In other words, the laws passed by Parliament were immutable. 
 The word “Senate” has its origins from “old man” so the line may be a pun on the etymology in relation to ‘Time’.
England in 1819