So is the "identifiable patient data" you're talking about only identifiable to NHS Digital and not the third party because it's anonymised (like I said in my original post)? Or is this part wrong: (or am I reading it wrong?)
The section you quoted refers to something done "before the data is shared with NHS Digital". Therefore if it did actually anonymise the data then it wouldn't be identifiable to NHS Digital either. Therefore it can't be the case that the process described in the section you quoted renders the the data identifiable to NHS Digital but not to the third parties they trade it to.
But it's a moot point anyway because it's explicitly stated that identifiable patient data will be traded with third parties. Whatever is done before trading it to third parties can't be anonymising the data because the data being traded is explicitly described as being identifiable patient data, i.e.
not anonymised.
Then there's the fact that anonymised data is only anonymous in isolation. Combining data sets will render it identifiable. But that isn't necessary when the data itself is identifiable, as it is stated to be in this case.
I wonder if identifiable is being used in the context that it could be traced back if required.
My clinical study has data which contains no personal information within the database, but there is a separate link file to allow you to identify patients if needed. (Accessible by only myself and the principal investigator). The database otherwise will just have data against a random identifier so would be meaningless outside of comparing the data collected in the trial.
That's a possibility if the official description of the scheme is using the words so incorrectly that it's meaningless or deliberately deceptive.
Your clinical study is a very simple example of anonymous data being de-anonymised by combining data sets. But the data in the database you refer to is not identifiable because
with that data alone it would not be possible to identify patients. The data being traded to third parties in this scheme is explicitly described as being identifiable, which means
that data alone is enough to identify patients.
If "identifiable" means "not identifiable by itself but identifiable if combined with other data", then all data is identifiable and it's meaningless or deliberately deceptive to make any distinction between identifiable and anonymous data.