There's been plenty of effort spent into estimates of benefits fraud, and by all account it is a tiny problem. Yes, it should be dealt with. But currently, the problems universal credit and other defects of the benefits reforms are causing are outright killing people.
Benefit fraud is currently far down the priority list of things that needs to be fixed, and that even goes for cost: The government has pushed things so far that you can look forward to a lot of tax money going to cover legal costs as a result of the huge and growing number of lawsuits the government is losing.
The government is complicit in far worse breaches of legislation related to the benefits system than fraudulent claimants are.
(this of course goes on the list of reasons why the government wants to get out of ECHR at any cost, since it's the only constitutional brake in the system)
The official method for estimating fraud rates is take a very small sample of claims, review the paper work and conduct an interview. of course this is never going to catch the majority of fraud!
Of course they'll never be perfect, but the official estimate would need to be off by at least an order of magnitude for it to matter vs. the harm done by government.
If it's that far off, there's at least half a dozen editors of major UK papers that'd be rubbing their hands in glee at the opportunity to further demonize benefits claimants by exposing more benefits cheats and/or by exposing flaws in the reporting. That this isn't happening despite both commercial and ideological gain to be had in doing it if they could, is to me a strong indication that the numbers aren't that far off.
I think the suggestion is that they'd be unable to detect it in many cases. And that's a fair point - of course some portion of fraudulent claimants will succeed in hiding it. I just don't think it's likely to be a sufficient portion to make much difference.
Benefit fraud is currently far down the priority list of things that needs to be fixed, and that even goes for cost: The government has pushed things so far that you can look forward to a lot of tax money going to cover legal costs as a result of the huge and growing number of lawsuits the government is losing.
The government is complicit in far worse breaches of legislation related to the benefits system than fraudulent claimants are.