Two quite different things are called a sort code. One is a branch code in the original sense, identifying a clearing point that corresponded to a building. The other is a whole institution code held by every customer of a bank. They look identical and they behave differently when you try to find out anything about them, which is why searches on a specific code produce such inconsistent results.
Branch codes and whole bank codes
In the branch model, the four digits after the leading pair identified a clearing point, and a lookup could return a street address because one existed. In the whole institution model, every customer shares one code and there is no branch to return. Both kinds of code are still in circulation. Nothing in the digits tells you which kind you are holding, so a lookup that returns an address for one and nothing for another is behaving correctly rather than failing.
What an address lookup really returns
Where an address comes back at all it is normally an administrative or registered office rather than a counter you could visit. Banks have consolidated clearing, closed branches and merged operations, and the address attached to a code in a directory follows the clearing arrangement rather than the customer. For the purpose most people need it, which is a form asking for the bank's address, the registered office the bank itself publishes is the right answer anyway.
Why this index gives a narrow answer
The directory that would return a name and an address for any code is a licensed commercial dataset. Rather than republish it, this index reads the banks' own published pages, quotes what each states about its own identifiers, dates it and hashes the page text so a later change is detectable. That produces fewer facts, each traceable to a page you can open. Where a bank publishes nothing, the entry says so instead of guessing.
Confirming this code for a payment
Get the institution's name from the payee rather than inferring it. Read the sort code and account number from one source that the payee controls, ideally their own bank's details screen rather than an email signature. Add the payee so the name check runs, and read the result. If a business has changed its bank, confirm by telephone on a number you held before the change was announced, because that is the scenario the whole check exists for.
Questions people ask about sort code 230580
Does every sort code have a branch address?
No. Codes held by a whole institution have no branch behind them, and a lookup returning nothing for such a code is correct rather than broken.
What address should I put on a form?
The bank's registered office as the bank publishes it. Payments route by code, so the address is a record keeping field.
Can I tell a branch code from a whole bank code?
Not from the digits. You would need the register, or you can simply ask the institution.
Is an address lookup a good way to check details?
No. An address proves nothing about who controls an account. Use the name check when adding the payee.