George Osborne wants benefit claimants to "do the right thing" and move into work. This, though, might not make very much difference to the economy.
The first question is: how many claimants don't want to work? As a rough pass, let's assume it is the number of unemployed who report very high subjective well-being; 9 or 10 on the ONS's 0-10 scale. 16.3% of the unemployed do so, which equates to 411,000 people.
Now, this could be an over-estimate, as it includes people who naturally have a sunny disposition, and folk who are happy because they expect to get work soon. But let's run with this.
Let's assume that all these could find full-time work at the national minimum wage. Let's assume too that employers are just waiting to hire so many (humour me). These folk would then earn £11885 a year; £6.19 for 40 hours a week and 48 weeks a year. £11885 multiplied by 411,000 gives us £4885m. Of course, employers would make a profit by employing these people. Let's assume that the ratio of profits to wages for these folk is the same as it is in the whole economy, at 37% (table D of this pdf); I'm ignoring diminishing returns here. This gives us £1807m of profits.
Add the two together and we have £6.69bn. This is 0.43% of annual GDP.
Of course, this is worth having. But it's not a massive sum. It's less than one quarter's of ordinary GDP growth.
Let's put this is context. If non-oil GDP had grown by just 1.5% a year since 2007Q4, the economy would be 9.6% bigger than it actually is. Scroungers and layabouts, then, cost the economy about one-twentieth as much as the recession has.
Of course, this is just the back of a beermat estimate and not a hard fact. You could get it higher if you assume there are more "scroungers" or if you assume that they could get higher wage work. Personally, I find these improbable - though I'll concede that Mick Philpott's intelligence and honesty would have equipped him well for a successful banking career.
You could increase my estimate in some other ways. You could claim that there would be powerful multiplier effects from "scroungers" moving into work. But it would be odd for defenders of fiscal austerity to suddenly discover big multipliers.
Or you could argue that low-wage workers are complements to higher-wage ones, so that the latter's earnings would rise as the former increase in numbers. But it would also be odd for supporters of immigration controls to suddenly adopt one of the economic arguments for open borders.
However, you cut it, then, the cost to the economy of layabouts - in terms of GDP foregone - is small.
There's a message here for left and right.
For the right, it's just plain wrong to think that "scrounging" is a serious macroeconomic issue. You might think it a moral failing. But don't confuse macroeconomics and morals.
For the left, you don't need to pretend that all benefit claimants are saintly victims in order to deny that scrounging is a serious economic issue. Even if we concede that there are tens of thousands of such scroungers, we can still maintain that getting them into work is not a top priority. A much bigger priority should be creating jobs for those who do want to work.