Check out Blake's early version of the poem and consider his reasons for changing some of its words, for instance, "dirty" for "chartered" and the insertion of "mind-forged manacles." The British Library also has interesting information on this poem such as what Blake would have "heard" from his house:
"The version of 'London' in the notebook was further revised before it was etched. 'Each dirty street Near where the dirty Thames does flow' refers to the narrow streets near Blake's home at 13 Hercules Buildings, Lambeth. Backing onto the Thames, they housed the labourers who worked for the local manufacturers, and the 'infants cry of fear' would have been heard by Blake emanating from the nearby Lying In Hospital and Asylum."
"We have used the published version for the reading of these poems 'The Tyger' and 'London' from Songs of Experience for the audio."