In my opinion (which is hopefully consistent with posts to other threads over the years) is that what we might call "hospital-based frontline biomed services" should come under the Nursing Directorate
at the Hospital or Trust concerned.
Why? Because they are the primary customer of biomed services (and therefore hopefully best placed to hear arguments about funding, budgeting, [lack of] resources etc.
All other options (coming under Estates, Facilities, Engineering or WHY) have been shown to fall short over the years, for various reasons that we need not go into here.
Myself, I have always found Senior Nurses generally supportive; whilst the Engineers (the Computer Gang ... and even Laundry Management) often see the biomeds as the "competition" (or even, it must be said, the enemy)!
But (IMHO) the real trouble with Technical Services in the NHS is its lack of overall structure.
As I have mentioned on here many times before, I believe there should support for the (First Line) hospitals available from a regional Second Line set-up (of mobile engineers, specialist workshops, management of service contracts etc.
) backed up by a central Third Line facility (providing *training, overall policy, "one-off" special facilities ... and all the **rest).
* Even if its contracted out to the likes of Avensys, Eastwood Park et al it should still be controlled by somebody!
** Such as central provisioning of equipment and spares, test equipment calibration, inspection services, pooled resources of rarely used (and expensive) test equipment, etc., etc.