In the poem "London, 1802," Wordsworth is scathingly critical of the city of London and of the English in general. He says that the city is "a fen / Of stagnant waters" and that the English have become "selfish men." Wordsworth wishes that London could return to the city he believes it was in the seventeenth century, when the English poet John Milton was alive.
When Wordsworth expresses his wish that Milton "shouldst be living at this hour," he means that he would like the spirit of Milton to be alive in London in 1802. Wordsworth says that Milton was a poet of "manners, virtue, freedom, power," whose soul was "pure as the naked heavens, majestic, free." Wordsworth also says that Milton's "heart / The lowliest duties on herself did lay," meaning that Milton was a kind and generous man who put others before himself, in stark contrast of course to the "selfish men" who inhabit the city of London in Wordsworth's time.
At the time Wordsworth wrote this poem, London was undergoing an industrial revolution. This revolution had a huge impact on Britain and on London especially. Cities like London were becoming heavily industrialized. The conditions of poverty were becoming more abject, in part because employers could now use machines to do the jobs that they would previously pay people to do. The air itself was becoming polluted with the fumes from the newly built factories. The complaints that Wordsworth levels against the English in this poem are likely related to the conditions consequent of this industrial revolution.