If it's a reasonably well known product for a well known condition (e.g. Enstilar for psoriasis) then I suspect ARN won't have a problem, it's used a lot over there. Strictly speaking you need a prescription, but I would have throught ARN would be OK with the NHS App. If you use the pharmacist that works a lot with a particular GP then depending on the systems the pharmacist can give you a print out of all your medication very easily and it looks so official that I can't see any security having a problem, it will have your NHS Number on it so it will link in with the App and your COVID jabs. That print out is used for those people who have lots of medication - some people have to consume 40, 50, 60 pills a day and the print out allows patients to make sonme sense as to what to take when. It's a bit daft just for one medicine but the pharamacist can extract the rprint out in seconds.