It was the four major banks and Macquarie that were the significant beneficiaries, to the extent of $116 billion, on our figures for wholesale bond issuance (including extendible CP issuance). This was split into $87 billion for international bond issuance and $29 billion for domestic.The individual totals are as follows, with domestic issuance in brackets: Westpac $25.9 billion ($8.2 billion); CBA $19.0 billion ($6.3 billion); Macquarie $16.6 billion ($2.1 billion); ANZ $13.2 billion ($4.5 billion) and nab $11.1 billion ($7.8 billion). The extent of this largess has led to criticism of the scheme and the banks themselves. Future Fund Chairman and ex-CBA CEO, David Murray, was quoted in the Financial Review this week as saying that the scheme has led to even further concentration of the banking sector. This is both in terms of the overall size of the big four banks and the increase in their market share in mortgages, for example. Murray went on to say that we went into the GFC without banks that are too big to fail but have not come out that way. This has placed Australia in a very precarious situation should another crisis evolve. Retiring BHP Billiton Chairman and former National Australia Bank CEO, Don Argus, has raised similar concerns, stating that some of our largest banks are nothing more than big building societies, given the extent of residential mortgage exposure on their balance sheets. With the RBA now vocalising increasing concern about the emergence of a housing bubble, some of the major banks could find themselves with significant mortgage delinquencies and defaults, should the bubble burst.Of course, these concerns have been raised regularly in the past and nothing has happened.Another concern is the refinancing risk that the scheme has created with the guaranteed debt having to be rolled over when it matures. Without a government guarantee some of the existing investors will not take up the new bonds: they are 'AAA' only investors.The potential size of this shortfall is unknown but it is known that much of the risk is concentrated in 2012 and 2014. By the time these maturities roll around credit markets may well be functioning normally.However, if this is not the case pressure will increase for covered bond issuance by the banks to be permitted. The ability to issue 'AAA' rated covered bonds may help to mitigate any potential rollover difficulties.