Let's start with shirkers,
Firstly the notion that anyone on benefits would not want to work, is laughable.
Being in work is far better paid than the pittance benefits pays out. I would rather be in work, sadly I am unable to do so, and if I was capable of some sort of work? Nobody would hire me except the sorts of exploitative bosses I will discuss in under the table work.
Most people who go to the job center desperately want to work, they want a job that pays a living wage, sadly many jobs do not pay a living wage, and the few jobs there are? Well, there's a lot of unemployed people chasing them.
Programs like http://www.channel4.com/programmes/dispatches/episode-guide/series-112/episode-3 only show that it is possible to slip things past the system. However just because someone can doesn't mean they will. There is little profit in remaining on benefits if you are healthy and capable of full time work, full time work pays better and doesn't get you belittled, attacked and abused by society.
In short, work pays better than benefits for pretty much everyone, claims that it doesn't are absolute nonsense. Though it should pay better, since there are still many working poor. If benefits were so much better, those people wouldn't be working.
Trust me, the majority of people who claim JSA are hardworking people who want to work. They are not shirkers, and all demonising JSA recipients does is harm the hardworking ones because typically it's honest people who get punished not shirkers.
As for under the table workers there seems to be a notion that somehow an army of people are working under the table and claiming benefits while laughing to the bank, a notion supported by programs like http://www.channel4.com/programmes/dispatches/episode-guide/series-112/episode-3
First up, let's examine why someone would work under the table:
I have had family and friends who have been put in the position of taking on under the table jobs or being unable to feed their kids. Your typical under the table worker in my experience isn't a fat cat, he or she is typically someone whose meager benefits cannot stretch far enough to cover things like food, clothing or heating, and who cannot get a legal job for some reason, they're typically desperate and needy, not greedy.
These people are not the stereotypical chav dressed in designer clothing with an iphone, an ipad and driving a mercedes benz (you couldn't afford that on most under the table jobs anyway!) they're the desperate mother of two who despite scrimping and saving can't afford to buy enough food to last the week, or who needs to buy her children new shoes, they're the father who can't afford his rent increase due to how small his benefits are but can't get a legal job, so chooses to work under the table rather than have his family become homeless.
The majority of under the table cash jobs are offered by unscrupulous bosses who know this.
This means that under the table jobs are:
1. Way underpaid, because you can pay crap wages to people who are desperate and needy.
2. Often break all sorts of labour laws, a desperate person isn't going to run to an employment tribunal if you don't give them legally mandated breaks or make them work ridiculous amounts of hours.
I know people whose efforts to feed their kids have led to them being exploited, assaulted and generally treated like crap. Are there fraudsters who lie to the jobcenter? Of course, but the vast majority of people who take on under the table work as desperate and exploited, not the stereotypical fraudster.
Ultimately under the table jobs would not exist if people could feed their family, or get a decent job. The real evil here is that people need to take these jobs and that exploitative bosses know this and exploit them.
The only way to change this is to promote job growth so there are enough jobs and to make all companies pay livable wages. The problem is not poor people, it's the state of our society.