National Australia Bank has shuffled a $3.8 billion pool of home loans into a special purpose trust in a process dubbed an "internal securitisation". Standard & Poor's disclosed the action yesterday by publishing a credit rating on the trust.A trend for banks began to undertake internal securitisations began to emerge in early 2008 in order to increase the pool of assets eligible for sale to the Reserve Bank of Australia to meet short-term funding needs.A string of banks put in place such structures over 2008 and into 2009, though they have become rare lately. MyState Financial undertook one such transaction this year.The NAB securitisation comprises loans originally financed by Challenger Mortgage Management prior to the takeover of that firm by NAB last year.One detail in the rating analysis published by S&P is that the level of arrears on this pool of loans, at around 2.0 per cent, is higher than the average level of arrears on loans monitored by S&P of 1.5 per cent.