The HSCIC isn't really new. It is a renamed / branded NHS Information Centre, although it previously didn't gather primary care (your GPs) records. What it did already do was gather secondary care (hospital admissions, A&E etc) and so already had all that data. This data was then accessible by PCTs for financial purposes / analysis and also by anyone else who coughed up the relevant funds and was deemed worthy. With the latest attempts to demolish the NHS however only the HSCIC has the legal right to access this non pseudonymised secondary care data. Not even the CCGs can currently do so due to yet another monumental DoH cock up and so GPs are currently being told they can't see the data for their own patients.
These third parties being talked of are the providers of the GP computer systems, the developers of things like SystmOne. It is my, possibly erroneous understanding as they might have a web based version now, that the only involvement they have is in writing the code to push the data to the HSCIC from their software.