As I see it, one of the problems with the benefits system is its complexity - instead of it all being under one roof, there are multiple agencies each responsible for different benefits. Because of this, the people who really need benefits often don't get what they're entitled to, to get their entitlement they need to
1. Know what their entitlements actually are
2. "Negotiate" with various inefficient and unhelpful agencies.
Conversely, the people who live on benefits permanently are very likely to get every bit of help going. One of their advantages is that their own social network is likely to include other people with the same attitude and the same lifestyle, and they share information and make sure that they get everything that's available.
Successive governments have tightened up the benefits system for years, in an attempt to prevent fraud, but from what I hear, the people who actually lose out tend to be the genuine cases, not the fraudulent claimants, who are expert at navigating the rules.
Then there are the fraud investigators, who are often unreasonable bullies who target people who make the tiniest of mistakes when claiming. All that these people seem to be interested in is getting convictions, they seem to apply no discretion and no common sense. Again, it's the innocent who suffer, the guilty know their way around the system.
Once they discover any irregularity, they claw back ALL of the benefits paid to that person as an overpayment, not just the amount actually overpaid. They may prosecute as well, and even if the person is found not guilty, they still claw back the benefits - they are judge, jury and executioner in these cases, and that is just plain wrong.
The government (of whatever political party happens to be in power) could easily change this, simply by creating a one stop shop for claimants, but doesn't. Of course, having a one stop shop wouldn't address the attitude problem that some of the staff have, but then that could be cured by turning some of the staff into claimants...