What's special about individuals who happen to be employed in the public sector or in receipt of welfare payments that makes it OK to intrude on their privacy in this way?
Like jumpcrisscross said.
Ideally, where every euro of taxpayers' money goes should be a matter of public record.
I doubt that that's what you actually think. For example, I doubt you want me to be able to ask the government how much money was spent on impotence medication for you. There's a trade-off to be made regarding personal privacy. Why do you think that trade-off should be made against certain groups of people?
You can have transparency and privacy, they are not mutually exclusive in this case. Government spent X amount of money on Y number of prescriptions for medication Z. You can determine if there needs to be further auditing if Y exceeds the projected number of prescriptions based on prevalence of conditions.