AFAIK this is not strictly true - the Charities Act merely makes provisions for regulations or bylaws which are intended to avoid annoyance to the public. While this may mean that tin-rattling is banned, it's not necessarily the case that it will be. On the issue of addressing the public, charity collectors are not allowed to ask for donations - that's all.

In any case, the point with the Big Issue is surely that it's not begging - it's a way for homeless people to earn money for themselves. If the woman outside Sainsbury's is not homeless, or is not earning her own money, that's another set of issues entirely.