I have read this thread with a lot of interest, the only problem with saying that each dog should have a licence is that there are so many diffrent breeds that have now been cross bred with others to make/try and get round all the rules.
If the Police get the report of a banned breed then a lot of the time the owner will argue the fact (and get help from some high profile people) that the dog is not of the banned breed . It is then down to experts to argue the fact in court in regards to what the dog is/isn't. This can go on for months/years and it all costs a shed load of money.
I do not believe that the banned/dangerous dogs should be in the country, but I have no idea what the answer is in regards to keeping check of them.
Sorry to go in.