I don't known if it's the same throughout the country (I mean, why would the NHS have one set of rules when it can have lots), but the dsn made it clear while I was being given the pump that it still belonged to the hospital, and if for any reason I didn't get on with the pump it would be reclaimed by the hospital. Not for reuse, but to stop people selling them on and possibly getting into trouble without having medical backup.
You can't buy a second-hand one (from my hospital anyway), because of some technicality with medical waste rules, so you may have to go straight to the manufacturer. You might still need a prescription to buy one, but if the consultant is OK with it he can write you a private prescription, not an NHS one. Good luck.