These ca. 200 trusts operate with a great degree of operational independence, though they are public entties.
The distinction is important because they are what makes the scale manageable, and it also provides resilience.
Though it also leads to inconsistency and the "postcode lottery" problem where the quality of treatment a patient receives for a specific condition can be extremely variable depending on where they live.
But it's better to have management failings contained to individual trusts, that are monitored, than to have these failing affect the system as a whole. Not least because it does allow patients going elsewhere as a last resorts.