I think that "London, 1802" does contain a healthy dose of nostalgia. The speaker, presumably Wordsworth, is longing for the days of John Milton to change what England is into what is used to be. This nostalgia ties into the Romantic tendency to long for what has passed, and the desire to bring back what once was into a condition of what is that requires it. The nostalgia here is for the poet Milton to return and help inspire a new sense of national character. Wordsworth himself feels that the "stagnant" and "selfish" nature of British character requires someone on the level of Milton to return and to bring back what once was into what is. It is here where nostalgia is most evident in the poem. For Wordsworth, the sense of contentment that was a part of Milton's life is something that he sees England as desperately needing at this particular point. The sense of being "happy, pure" is in stark contrast to the growing appetites of England, and with it a willingness to forgo the simple pleasures consciousness has to offer. In this, there is a yearning for what was and through this, Wordsworth demonstrates a great deal of nostalgia for the past.