Westpac will spend billions of dollars over four years to cure more than a decade of underinvestment in its bloated and slow technology stack, bringing its brands onto a single platform and decommissioning 120 systems under its new Unite strategy.

The bank’s chief information officer, Scott Collary, said the push aimed to eliminate risks and costs that had hamstrung the bank for 15 years since its acquisition of St George at the height of the global financial crisis.