Pharmacuticals/Medications

Hi I hope someone can help me here. Can someone tell me if medications taken in another country and prescribed by physician be carried and taken into UK (England and Scotland mainly) I realise some medications unavailable in UK but how about when on visit can it be authorised during that period time? Thanks in advance to all who may be able assist me on this matter. 

All the info I have read has advised that you get a written note from your Dr stating the meds are authorised for genuine use, although I have travelled with prescription meds without a letter and never had a problem - I figure the info on the label is usually enough.

I do think it depends on the medication though, when my MiL came over, she was on Oxycontin and I am aware that it has huge re-sale/abuse value, so I made her get that letter from her physician which turned out to be quite useful as she had mis-calculated the amount she needed and was about to run out and a quick trip to my own GP mean't he could prescribe her more with a quick call to the U.S - he also only charged her for the cost of the prescription ( I think that's £6.40 or something now here) and she wished she had got more!  (Ask for a private prescription if you ever find yourself in that position.)

HTH - or at least makes sense.