I haven't worked a shift since Decemebr 2006 but I worked as RMN for 8 years beforehand.
One of the major sources of money wastage in hospitals across the board was that upon admission to hospital - patients were always asked to bring in all of the medication they were currently taking, so that the doctor on duty could use the information label on the packaging of any prescription medicines in order to transfer them verbatim onto the hospital 'treatment sheets'. The sheets acted not only as charts for us to record and sign for medicines if they were administered (and to record instances when they were not i.e. a refusal), but were in themselves legal prescriptions for current inpatients.
This was always seen as the most efficient way of transferring everything over as accurately as possible, as the patients may not have any other information regarding this such as photocopies of current outpatient scripts or recent GP letters with the entire treatment regime as of course many unplanned admissions occur out of hours and in these instances it could be up to 72 hours before we could confirm any of this with the GP directly (even if your subs scripts are issued by a specialist addiction service your GP should still have an accurate and current record of the drug and dosage to be taken).
After the patient was admitted, they were (and of course still are) not permitted to free access to any medicines they take so that everything that someone is administered during an inpatient stay is recorded as described above, as all responsibility for this is part of a nurses standard duty of care, making them legally accountable for anything that is or isn't taken, prescribed or unprescribed.
Once the doctor had finished their part of the admission process and re - prescribed any medicines that were to continue during their stay, we would basically remove them, throw them in the bin (of course, the 'bin' being a secure storage box for their collection and destruction by pharmacy staff) and we would then use our own ward and pharmacy stock from the drug trolley.
With the amount of unused medicines being dispensed and then thrown away being a major source of financial waste for the NHS top to bottom (a distance that decreases of course as more and more statuary services are sent out to tender) one small area that they could stop this was by changing the process above and introducing personal locked drug cupboards for individual patients so that they could use up there own supply before the hospital pharmacies had to dispense more drugs for continuing treatment.
In many hospitals now, the cupboard is usually located next to an individuals bed so although they may not have access to it they can at least monitor there own supplies as they are dished out, and from a legal perspective, even if your prescription medicine is not accessible to you under these circumstances they are still your own property and anything that has not been used should be returned upon discharge if still needed and prescribed.
Of course, cock ups do happen but if you can get it sorted at this late stage - any anxieties you may have about you original concern can be alleviated by having a responsible adult (preferably a direct relative such as a parent, sibling or spouse) hang on to you subs and only give the ward nurses a couple of days supply at a time, but as but as buprenorphine is a class C, schedule 3 drug it is very important that you have this arrangement firmly in place before you are admitted, as otherwise they could be liable to prosecution for being in possession of the drugs or even liable for their supply.
I hope that this is of some help but it is important to try and ensure that you have made contact with the ward staff prior to your admission as local policies and procedures covering this area can vary greatly between different inpatient settings.