SPOT the villain: Google, Starbucks, Vodafone, Amazon, alcoholics, drug addicts, fat people.

If you are David Cameron the choice is clear.

The first four - giants in business, midgets in tax - can do no wrong, while the last three are obviously asking for trouble.

In the PM's world, and that of HM Revenue & Customs, firms such as the first four are to be handled with kid gloves and a quiet word.

But people who fall into the other categories, if also on benefits, need sticks not carrots.

Hence Cameron's announcement yesterday, part of his "moral mission" on welfare, of a review which could see thousands who cannot work because of obesity, drug or alcohol problems lose benefits if they do not seek treatment.

Now spot the magic number.

The Department of Work Pensions estimates benefit fraud in 2013/14 cost £1.2bn.

The "tax gap", the difference between what is owed to the Exchequer and what is collected by HMRC, stands at £34bn.

Again, the two figures seem to inspire markedly different emotions in the PM and his ministers.

Cracking down on benefit fraud is a priority; collecting the UK's tax more of a luxury.

Cameron's announcement yesterday was the opening salvo to a week of welfare announcements from the Tories designed to tap into, and undoubtedly stoke, public resentment over benefit levels.

Coming after a week in which several Tory donors cropped up in the HSBC tax scandal, the timing could not be worse for Cameron, as it throws his government's attitude to the rich and the poor into the starkest possible contrast.

There is no financial logic to prioritising benefit fraud when the sums are dwarfed by tax avoidance schemes open only to the rich.

That is pure political ideology on show.

It is also a green light to banks and their high worth customers to keep pushing their luck, and a coded signal to HMRC not to bare its teeth.

Cameron may not feel it yet, but others such as Ed Miliband and Nicola Sturgeon sense the country is at a tipping point on tax.

As with the MPs' expenses scandal, the scale of wrongdoing can no longer be ignored or excused.

If HMRC is to retain public confidence, it must bring prosecutions against tax evaders.

There is certainly no shortage of candidates.

As to David Cameron, the electorate can always spot the villain, even if he can't.