In respect of the comments re mental health problems, many people with problems of addiction (whether substance abuse or gambling) do need help and do deserve to be looked after. They of course must be willing to accept this and generally understand that their actions not only hurt themselves but those close to them and the public in general.
Sectioning is not the answer unless the person presents a serious risk to themselves or the public. These days with better CMHTs and an improving IAPT service, the necessity for sectioning is reducing - which is a good thing. People don't prosper or recover when isolated from the world.
If someone is presenting as a nuisance or causing problems, it is important to report to the police if you think there is a problem and the police can deal with that issue - whether 999 or the local station etc.
It's a bit hippy of me, but that's how I am and I think we all need to be aware that whilst people like this man are creating a social nuisance, you can guarantee that they would be horrified at themselves if they were able to understand the impact.
In respect of Melissa's problem, I agree to not confront and seek help from a passer by or a shop worker/owner. Safety in numbers...and not violent responses.
Hippy lecture over.
Peace and love.
Andrew.