I don't believe Honor Oak should count as part as FH, even if it's in the same postal district. It is defined principally by its railway station, like most places in London. It is in Crofton Park ward, not FH or Perry Vale. On the rare occasions I visit it, it feels funny and foreign to me. I suspect that culturally and economically it is closer to trendy and metropolitan Brockley than to suburban lower middle class FH.