The ACCC's latest inquiry into the banking sector will trawl over mortgage pricing terrain that the competition regulator has been traversing for several decades. The ostensible motive for the new inquiry - the failure of regulated lenders to pass on the full benefit of Reserve Bank's official rate cuts this year -  reflects heightened public concern that big banks are continuing to fatten their bottom lines at the expense of home borrowers. The major banks' partial transmission of the October rate cut drew hostile reactions from Treasurer Josh Frydenberg, Prime Minister Scott Morrison and their counterparts in the Labor opposition. However, the veracity of those reactions was questioned last week by leading business commentators such as Michael Pascoe and Stephen Bartholomeusz, who each alerted their readers to the verifiable reality that most deposit taking institutions - large and small - suffered severe margin contraction in the last 12 months. While Frydenberg and other politicians savaged the major banks for conveying to borrowers only 12 to 15 basis points of the RBA's 0.25 per cent cut, none were prepared to acknowledge that margin pressure had forced most credit unions and mutual banks to do the same. Frydenberg said yesterday that his new inquiry would "lift the hood" and "get to the bottom" of the controversy over mortgage pricing. "The Australian public are asking are they actually getting the best possible deal from their banks," he told the ABC. "We've got a two trillion dollar residential mortgage market, the big four banks have locked up about eighty per cent of that market and we need the ACCC to use its particular powers to compel documentation to lift the hood and to get to the bottom of this issue." One slender benefit, Australian Banking Association CEO Anna Bligh pointed out, may be "a great deal more accuracy of what Australians are actually paying for their mortgages". But there are several aspects of the new inquiry which indicate Frydenberg is merely grandstanding in the face of the public concern, rather than genuinely canvassing the factors that determine how a mortgage is priced. Most small ADI lenders didn't pass on all of the RBA cut - an awkward development for the government that is prone to reserving its public rebukes for the major banks. In the ministerial direction that establishes the new inquiry, Frydenberg makes no request for the competition regulator to stump up recommendations in its final report to the government. Scott Morrison, as treasurer in May 2017, did a similar thing when he asked the ACCC  to examine differences in the way the major banks were pricing mortgages for new and existing borrowers. While the report from that inquiry that was published in November last year generated valuable insights into the repricing of