Hi
The London boroughs of Barking, Newham, Redbridge and Waltham Forest officially became part of Greater London only in 1965. Before that those areas now covered by the four London boroughs were part of the county of Essex.
The family history society which covers the East End of London is the 'East of London Family History Society'. They have produced information on their website on the whereabouts of parish registers in the area.
http://www.eolfhs.org.uk/area/parishes/Generally if it is Hackney and Tower Hamlets the parish registers are held at the LMA and therefore covered by Ancestry and if its parishes in the four London boroughs previously mentioned, they are held either with the local boroughs archives or at Essex Record Office if they are in fact deposited. If the registers are held at Essex RO then the local borough archives may hold microfilmed copies and indexes.
Parishes concerned in the four London boroughs would be these from the East of London FHS list
Aldborough, Barking, Barkingside, Becontree, Canning Town, Chadwell Heath, Chigwell, Cranham, Dagenham, East Ham, Forest Gate, Goodmayes, Havering, Hornchurch, Ilford, Little Ilford, North Woolwich (part), Plaistow, Rainham, Romford, Seven Kings, Stratford, Upminster, Upton Park, Victoria Dock, Wanstead, Wennington, West Ham, Woodford.
Regards
Valda