Blackfen is an area of South East London, England, within the London Borough of Bexley. It is located north of Sidcup and south of Welling. Prior to the creation of Greater London in 1965 it was in the historic county of Kent.

The London Borough of Bexley is a London borough in south-east London, forming part of Outer London. It has a population of 248,287. The main settlements are Sidcup, Erith, Bexleyheath, Crayford, Welling and Old Bexley. The London Borough of Bexley is within the Thames Gateway, an area designated as a national priority for urban regeneration. The local authority is Bexley London Borough Council.