The London Plan download section
Housing
3A.10 Negotiating affordable housing in individual private residential and mixed-use schemes
Boroughs should seek the maximum reasonable amount of affordable housing when negotiating on individual private residential and mixed-use schemes, having regard to their affordable housing targets adopted in line with policy 3A.9, the need to encourage rather than restrain residential development and the individual circumstances of the site.
Targets should be applied flexibly, taking account of individual site costs, the availability of public subsidy and other scheme requirements.