Require developers to make their viability assessments public if they claim they cannot meet council targets of affordable housing in new developments.

Current planning law states that if a developer will make less than 20% profit on a new development, they can ignore a council's regulations about building affordable and social housing.

Leaked documents from several developers have shown that the maths they use to work out their profit margins are purposefully misleading, allowing them to claim they will make less than 20% profit on a development by undervaluing the prices of the houses they will sell and over-costing the labour.

To combat this Islington, Greenwich, Lambeth and Bristol councils have introduced a policy that forces developers "viability assessments" to be made public.

By bringing these dodgy maths into the public domain, Councils, campaigning groups and individuals will be able to hold developers to account and force them to use more honest maths.