By Borough
Double Storey Extension Drawings by London Council
Borough-by-borough guidance on double storey extension drawings — local conservation areas, Article 4 directions and validation quirks for each council.
Waltham Forest
London Borough of Waltham ForestHackney
London Borough of HackneyHammersmith & Fulham
London Borough of Hammersmith & FulhamCroydon
Croydon CouncilRedbridge
London Borough of RedbridgeEnfield
London Borough of EnfieldHounslow
London Borough of HounslowSutton
London Borough of SuttonHavering
London Borough of HaveringBexley
London Borough of BexleyHillingdon
London Borough of HillingdonBarking & Dagenham
London Borough of Barking and Dagenham
London Borough of Waltham ForestHackney
London Borough of HackneyHammersmith & Fulham
London Borough of Hammersmith & FulhamCroydon
Croydon CouncilRedbridge
London Borough of RedbridgeEnfield
London Borough of EnfieldHounslow
London Borough of HounslowSutton
London Borough of SuttonHavering
London Borough of HaveringBexley
London Borough of BexleyHillingdon
London Borough of HillingdonBarking & Dagenham
London Borough of Barking and Dagenham
Double Storey Extension Drawings guides that apply in every borough
These are the same in all 33 councils, so they are worth reading once rather than borough by borough.