Statutory Instruments [secondary legislation] such as the Building Regulations 1976 HERE, did not apply to London as elsewhere in the country until the Building Act 1984.
Some information about Local Acts HERE
HoL 1999 Housing, Quiet Enjoyment, Nuisance HERE
"But they did not contravene the bye-laws in force at the time"
The Building Act 1984 replaced the previous system of local bye-laws with nationally applicable regulations made by the Secretary of State for the Environment.
The Building Regulations 1985 (SI 1985/1065) contained for the first time a requirement that walls and floors which separate one dwelling from another should resist the transmission of airborne and impact sound: see Part E of Schedule 1 to the Regulations.
Similar provisions are now contained in the Building Regulations 1991 (SI 1991/2768). But the regulations apply only to buildings erected or converted after they came into force."
" Byelaws are local laws made by a local council under an enabling power contained in a public general act or a local act requiring something to be done – or not done – in a specified area. They are accompanied by some sanction or penalty for their non-observance."
If validly made, byelaws have the force of law within the areas to which they apply. Generally byelaws are overseen by the relevant government department or confirming authority who has policy responsibility for the subject matter." HERE
The Local Government Act 1972 HERE gives instructions about the making of local government bye laws [also called Local Acts]
Part XI  General Provisions as to Local Authorities HERE, under the cross heading Byelaws are sections 235-238 HERE
Sections 262 Local Acts and instruments HERE
Going back in time 40 years or so, the London Building Act 1930 HERE came about 12 years after the end of world war 1 [1914-18]
The whole Act came into force 1 October 1930.
Part VI  Construction of Buildings sections 57 - 88
London Building Acts [Amendment] Act 1939 HERE
London County Council [General Powers] Act 1948 HERE
Local Government Act 1972 HERE
Greater London Council [General Powers] Act 1974 HERE
Building Control Act 1966 HERE
Housing and Building Control Act 1984 HERE
Building Act 1984 HERE
2.17 approval under the London Building Acts and the associated bye laws was the responsibility of the Greater London Council [GLC].
4.1.13 The London Building Acts 1930 - 1939 gave powers for secondary legislation to be produced in the form the London Building [Constructional] Bye laws. The BLs would have comprised:
The Public Health Act 1936 HERE
Statutory Instrument 1057 HERE
1972 No 317
BUILDING AND BUILDINGS
The Building Regulations 1972
The below Act exempted some buildings from building by-laws.
Public Health Act 1936 HERE