The quality of the loan book acquired from the takeover of Bank of Western Australia appears pretty poor. Based on the data provided in the Commonwealth Bank profit yesterday, BankWest has the equal highest proportion of impaired loans of any significant lender.Suncorp is BankWest's companion in this ranking based on data disclosed by Suncorp last week, while BankWest's former owner, HBOS (now owned by Lloyds TSB) has the highest percentage of problem loans, at 1.4 per cent of assets (or did, based on simplified accounts for June 2008 disclosed at the time of the takeover).The impaired assets of BankWest appear to have deteriorated materially between June 2008 (and again based on simplified accounts published in October by CBA) and December 2008.CBA said its own ratio of gross impaired assets to total loans and receivables was 0.48 per cent at December 2008. Including BankWest this ratio rises to 0.58 per cent.The BankWest portfolio alone has $770 million in impaired loans, out of $59 billion in assets.While disclosing some details of the impact of BankWest on its financials, CBA is yet to finalise many accounting details.CBA elected to equity account the profit of its 100-per-cent-owned subsidiary (owned since mid December). Final accounts for BankWest are yet to be prepared.This did not stop CBA recognising a gain on the acquisition of BankWest of $547 million in the statutory profit.