Registered Charity Numbers

I was in my local supermarket yesterday afternoon and was about to place my change in a charity tin, there were a few there (Paul Cunningham Nurses, S.A.T.S, K9 and La Marina Animal Welfare) when I noticed there was no Registered Charity Number on one of them, which belonged to a group called PAWS.
If they are a charity and asking for public donations then surely they should be registered legally right? I think donating to charities is very important but I for one would like to know my money is going somewhere legitimate. Does the Town Hall deal with matters like this as I think I would like to check this out?