I havnt been in Accy for Crimbo since I moved up here so dont know what musician you are on about Magpie. Micks right about the licence sadly and he does need one but I wouldnt class it as begging. He is providing a seasonal service and if he is causing no trouble for anyone and they are enjoying he should be left alone. The season of good will and all that.
It seems that they have to apply for a licence but it varies council to council.
http://www.vocalist.org.uk/busking.html
As for the Big Issue selling that can be a bigger pain than busking but as stated is licenced. It has got to the point that if I visit Glasgow or Edinburgh I buy one and carry it to get a bit of peace as there are that many of them especially at this time of year.