What exactly is happening in the bowels of the American mortgage market? That is a question that investors around the world have often asked in the past three years, with a mixture of bafflement and alarm.

Now they need to pose it again. For this spring, something of a paradox is hanging over the mortgage-backed securities world. At the end of this month, the US Federal Reserve is due to freeze its programme to purchase Fannie and Freddie agency MBS that it implemented in the wake of the financial crisis. Logic might suggest that could potentially deliver a jolt to the market.

After all, the reason why the Fed introduced the programme in the first place was because the US securitisation markets froze during the financial crisis, removing a vital source of funding for the American mortgage world. And thus far, at least, there is still precious little evidence that the securitisation market is ready to flourish again.