What is a “nervous breakdown”? So many responses here to what could be any cause (unless I’ve missed a qualifying email by OP).
“Nervous Breakdown” is not a diagnosis, it could literally mean anything and therefore if you really want to know what prognosis is for full recovery you’re either going to have to divulge the diagnosis the NHS psychiatrist or his GP has made , or go talk to his professional medical team for an answer
Mental health diagnosis can be anything and extremely varied in terms of full recovery. Some , usually described as “severe and enduring” require life long medication, which at the right amount and with strict compliance (which is unlikely in many cases) could control symptoms of some to allow them to live a full and rewarding life. Others will struggle to even work. My ex was one who, despite being fairly compliant with meds, never was able to work again in the last 20 of our 30 year marriage.
other mental conditions are not described as enduring, and with right drugs and therepy can enable people to make full recoveries. But that usually takes a lot of time (6 months min IMHE) . Getting the right therepy and right therapist is incredibly hard without money and access to private treatment.
mental health services, both primary and secondary (who treat the severe and enduring cases and those sectioned or inpatient) are in a dire state. Proportionally less medics want to go into this medical field, and funding is still much lower than physical illnesses. Generally all there is money for is drug therapies. Youhave to fight long and hard to get the right psychological intervention therapies.
if you genuinely want help, OP, you’re going to need to be way more specifics about his diagnosis - he clearly has one if he’s on meds.