HDFC BANK LTD-ADR | HDB.US – US40415F1012
When looking at ADR’s (or other depository type interests/receipts such as ADS’s), the listing or trading of the actual ADS or ADR is irrelevant. All that matters is the qualifying status of the underlying shares. If the underlying shares are ISA qualifying (because they are listed on a recognised stock exchange or admitted to trading on a recognised stock exchange in the EEA, including the UK), then the ADR (or ADS) automatically qualify (regardless of its listing status).
I can find no evidence on the company website (or any other website) that the underlying shares are individually listed or traded on a recognised stock exchange so, on that basis, the depository shares will not be eligible for ISA inclusion.
The ISIN code US40415F1012 relates to the ADR despite the confusion on the Börse Frankfurt Stock Exchange referring this as common shares/equity. The title of the ISIN also states this is an ADR. The London Stock Exchange (link below) also refers to this as an ADR.