A Community Network for Bowes Park and Bounds Green
This is par for a property of this age - the electrical service probably also used wire fuses in both live and neutral phases.
Does the property have (had) a gas supply? At the date of the property's electrical installation earthing would have been provided by a connection directly to the gas pipe. The original gas supply in the street and in the house may (should) have been changed to yellow MDPE Alkathene piping; when this was done the freeholder/tenants of the flat would have been served a notice requiring the provision of the separate electrical earth connection.