I guess the first starting point for that question is whether it is to do with the UK vs AUS banks themselves as a market (reliability of earnings, growth opportunities etc) or whether it is an Australian investors difference; that asx investors value banks reliability much more highly, or thirdly is it directly correlated with the strength of AUD previous decade. The US seems to have bank P/B ratios averaging 1.2-1.3 which is somewhere in the middle.