The correct title of this poem is England in 1819. I tried to move this question to a different group- "England in 1819" -but was unable to do so for some reason. Nevertheless, there is such a group here on eNotes, at the link below.
This poem is a political poem. It describes the state of the nation, England, in 1819. The king, King George III, was crazy and dying at this time. England is a nation of people "starv'd and stabb'd in the until'd field." The people have no hope. They are oppressed by the very leaders who are supposed to be leading them. Shelley shows his contempt for this situation. The structure of this sonnet is very abnormal as far as rhyme scheme and meter, illustrating the disorder of England as well (mark the feet in the poem and the end rhyme and you will see this).
There are lots of wonderful figures of speech:
Princes, the dregs of their dull race, who flow
Through public scorn--mud from a muddy spring,
In these lines, there is a metaphor - comparing the royalty (princes) to the dregs of wine - which is the cruddy stuff at the bottom of the bottle that no one wants to drink. The metaphor is extended by comparing the royalty (in particular the king) to a liquid that is flowing through "public scorn" -- the mud of public scorn. Pretty strong imagery, huh?
Now that you know the theme, can you find other figures of speech? Look for ways in which Shelley compares the king and the political climate in England to leeches, prey, violence, weapons, etc.
See the eNotes link below to help you further.