Record Benefit Fraud

Hard to take in this, the largest benefit fraud in British history has been busted, but it took a foreign policeman to start the investigation when people who were usually poor, suddenly started splashing the cash. In one case, someone had $750k GBP in a suitcase in his house. 

How does this happen, how did the British authorities fail to detect what was going on? 

It reminds me of the benefit fraudster in Auckland who ripped off the taxpayer by having multiple fake names receiving unemployment benefit. He invested a lot of the money in things like Apple shares, and when busted he'd grown this fraud into a small fortune. In that case, the taxpayer ended up ahead on the deal. Instead of going to prison, they should have promoted him to looking after NZ's pension system, we may all be in clover today if they had.