Any attempt to enforce account number portability on the financial sector would impose "horrific" costs on banks, according to Westpac's chief information officer, Bob McKinnon, who warned that overseas experience suggested such a move would not deliver sufficient value to justify the investment.With Bernie Fraser scheduled to deliver his report to Government on account number portability shortly, McKinnon's comments gives a clue as to the massive bill the financial sector would face if account number portability is mandated.Speaking at a CEDA lunch in Sydney on Friday, McKinnon explained: "The fundamental thing is the uniqueness of the account number and at the moment even within a bank the particular account number isn't unique, but it's linked to the BSB number."At St George they only have one BSB, but for other banks the same account number would apply to many customers."It was the unique combination of the BSB number and account number that was used to identify an account and link it to an individual, he explained. "In order to have portable accounts you'd need unique account numbers and in order to do that you'd have to totally dismantle the current basis by which banks number accounts, [which is]... the BSB system. "That system is built into the DNA of technology of every bank. You can certainly solve the problem - but only at a horrific cost," said McKinnon."Then you have to ask the question: does the value you bring from doing this justify the horrific cost? And I can assure you it would be a horrific cost."I know in the UK they started off on this journey and my recollection is that after truly understanding the problem, truly understanding the cost, and truly understanding the benefit they would get, they abandoned the process."Westpac has spent around A$500 million over the past four years improving service management and stabilising its technology.The bank has a further $2 billion earmarked for a series of IT investments, dubbed strategic investment priorities, which will eventually include a core banking systems' upgrade.So, the addition of extra "horrific" costs to permit account number portability is clearly unpalatable to the Westpac tech tsar.