I've met people that were very open about scamming the system.
I once knew a person, that went to London 17 years ago from another Country. He managed to get a not fit for work benefit and housing. His later then 'wife', they never got married but have a child together and live together, got some illness. Never met her, he was saying that was a genuine illness and not like his and she can't work.
So that person that I mentioned above, owned a car and a motorbike. Not sure if those items were under his name or not. He also worked at a car mechanic shop for money under the table.
In the 4 years I knew him, he was never caught, nor anyone went to his supposed house to check if he is there or what he is doing.
That guy was literally skimming the system for money without any control. At some point he and his 'wife' found out about another scam that they could run, if she gets evicted by her landlord (both of them were getting housing benefits, but they were presenting that they were staying at 2 different properties while he was staying at her house) she could somehow get a free house. So they decided to bring a dog home so that the landlord sends them out. They got send out. She was put into a b&b with her daughter for a few months, while he was staying at the other house the benefits was paying for and then I've no idea if the scam worked or not.
To be very and completely honest, I did look into how I can report that guy, just because I didn't find it fair, that I am paying taxes and there are people like this person on the article that really need the money, and you get those people that just scam the system. All I got from googling how to report someone, was that the reporting system sucks so much that the HMRC won't really do much about it.
That sort story is just there to show you whats wrong with the system in general.