Insulin is one of the drugs most commonly associated with medication errors. (As well as being a drug of choice for some HCPs intent in doing harm). It's usually stored in a locked drug fridge on the ward but most diabetics bring their own into hospital with them, or have more of their own dispensed by pharmacy and kept in the personal locked bedside drugs cabinet which most hospitals have now. Most diabetics will self administer their insulin whilst they are in hospital unless they are too unwell to do so. They sensibly don't trust the nurses to get it right.
There is certainly a case for putting additional security around the ward stocks eg they could have two locks on the fridge requiring two separate keys held by different nurses so that a single nurse could not access it alone. Or these days it would be easy to have an electronic system, which obviously would give a record of every time it was accessed. Especially on neonatal and paediatric units where the patients are particularly vulnerable and often critically ill.
As for controlled drugs, despite all the many security systems in place, people do still manage to misuse them.
In my hospital earlier this year it was found that fentanyl was going missing from the emergency anaesthetic trolley. This is literally the only place where the drugs are kept not locked up - there is an emergency theatre with an emergency anaesthetic trolly, kept ready for instant use, hence not locked away. A junior anaesthetist was the identified culprit.
And sadly the father of one of DD's friends was an anaesthetist who knew exactly which drugs he needed to misappropriate for tragic reasons.
And entirely different circumstances and not in the U.K. but this is an interesting podcast where the nurse at Yale university hospital IVF clinic was substituting the fentanyl for saline and misusing the fentanyl. It meant patients having IVF egg collection did not have adequate analgesia. Lots of parallels around the hospital being uncooperative and unhelpful with enquiries and really, generally a shocking response from the hospital.
podcasts.apple.com/gb/podcast/the-retrievals/id1691599042?i=1000618732469