Data Protection and Digital Information Bill

I have a question. I am slightly puzzled about the difference between data collection and surveillance. Surely the collection and gathering of data would be to enable officials to survey someone’s bank account. If that is not the case, what is the purpose of collecting the data if not to interrogate the behaviour of an individual to understand how their money is being brought in and spent, so that the department can exercise some judgment over whether the individual is revealing the truth about their income and outgoings?