Chancellor Street was a road in the heart of London proximate to the Royal Hope Hospital. It was the site of Martha Jones' first encounter with the Tenth Doctor. She saw him jump out in front of her, remove his tie, briefly speak to her, and walk away. Though she didn't know it at the time, this odd behaviour in Chancellor Street would later prove to her that the Doctor could indeed travel in time. (TV: Smith and Jones)
Behind the scenes[]
Chancellor Street does in fact exist in London W6, within the Borough of Hammersmith and Fulham.