The first foreign backer for SIBs has now emerged - slither forward the Giant Vampire Squid of banking, Goldman Sachs.
Under SIBs, big investors put money into social services, investing in welfare provision run by charities or companies.
When "savings" are calculated at the end of contracts - from the number of folk kept out of prison or in work or similar social benefits - bondholding banks get a payoff. Consequently, SIBs always involve privatisation. Banks and bondholders cannot invest in publicly owned probation services or council social work departments.
These services have to be handed over to either private firms or charities to make them "investment ready."
SIBs are being trialled in Peterborough. Bond investors will be paid if a charity can prevent ex-prisoners from returning to jail.
David Cameron's high-profile "rehabilitation revolution" speech in October in effect announced an expansion of SIBs across the welfare sector, long before "Peterborough experiment" results are evaluated.
Goldman Sachs is joining in. New York Mayor Michael Bloomberg announced in August that he was copying British SIBs.
Goldman Sachs will invest $9 million in a scheme to rehabilitate teenage New York prisoners. If the youngsters don't return to jail, Goldman get profits.
George Osborne has admitted that the private finance initiative was a terrible deal that left the public overcharged by private companies building and running hospitals and schools.
Instead of bringing new, supposedly efficient ways of running public services, PFIs allowed companies to rip off the public sector, overcharging for poorly run services. Osborne has offered an unconvincing makeover for the PFI as a solution.
And now he intends to use PFI-style methods even more widely.
SIBs effectively use PFI methods in social services - if contracts are badly written, investors could squeeze cash out the government for poor results.
The enthusiasm of Goldman Sachs is a bad omen as it is expert in questionable contracts - like its role hiding Greek national debt before the euro crisis or in the subprime mortgage crisis, for which it paid a $60m fine in Massachusetts.
At the 2010 Tory conference I heard Prisons Minister Crispin Blunt announce international interest in the bonds, saying: "Rather like privatisation in the '80s we may find something that leads the world."
But back then Blunt also warned of possible dangers that "investors end up taking the public sector to the cleaners because they find a model that always pays out."
By this year's conference, such caveats were gone - I sat in a breakfast meeting at the Tory's Birmingham conference where "Civil Society" Minister Nick Hurd enthused about "social investment, a blend of social impact and financial return" being a "very big opportunity," which he wanted to "sweeten" with tax advantages and involve "serious money."
The City of London "social investment" pamphlet given to delegates at the meeting showed similar enthusiasm for bringing banking's brilliant record to bear on welfare, declaring: "No longer can we consider philanthropy as the only way to create social benefit returns" and arguing "the challenge is to make investors and investees ready and able to deliver lasting benefits to society, whilst offering acceptable financial returns."
With Goldman Sachs and the City of London determined to get into welfare, what could possibly go wrong?
George Osborne might be cutting the dole, but his friend Iain Duncan Smith is still handing hundreds of millions to the Work Programme contractors. So while the unemployed might suffer, the firms are cashing in.
This seems to be particularly good news for Emma Harrison, owner of A4E, the "benefit-busting" firm that doesn't actually get people off benefits.
This year she has taken another £1.375 million dividend out of A4E, money that all comes from government schemes to get the unemployed back to work.
Which is particularly startling since the latest figures show her firm failed to meet minimum performance standards and actually got fewer people into work than would have found jobs without A4E's help, according to official estimates.
But Harrison's money and performance have never been closely related. She brought her firm into disrepute with the revelation she had taken an £8.6m dividend in 2011.
Since then A4E has tried to minimise the "reputational damage" by having her resign from the board - although she still owns the firm and can tell the board what to do at any point, so this is a bit of a fiction.
Harrison tried a recent comeback tour of Fleet Street and the TV studios, hiring Max Clifford to help her return.
Both Harrison and A4E tried to give the impression that last year's £8.6m dividend was a "one-off."
Harrison told the Mail the big windfall was "not a dividend of one year, it was a result of 25 years of work."
She told the Sun it was "an exceptional payment after 25 years of investing tens of millions of pounds in that company."
A4E's ex-Tory Central Office lobbyist Jonty Olliff Cooper said the big payment was "done after 20 years of work."
But in fact, while the 2011 dividend was especially big, Harrison had been taking millions out of the firm before then.
Between 2007 and 2010, she took around £6.1m in dividends out of A4E. Add the 2011 bumper dividend and the latest payment, and over the last five years Harrison has siphoned off around £15.8m from A4E, all from cash paid by the taxpayer to help the unemployed.
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