DUBLIN—Ireland’s central bank on Thursday fined NatWest’s Irish business, Ulster Bank, a record 37.8 million euros for overcharging mortgage customers, some of whom lost their homes after being denied their right to a cheaper “tracker” mortgage. The penalty was almost twice the largest fine previously laid down by the regulator on any institution, a 21 million euro reprimand for permanent tsb in 2019, also for failing to offer customers a mortgage that tracked the European Central Bank rate that has been at or close to zero for almost a decade. Irish banks have paid out almost 700 million euros ($826.84 million) to compensate 40,000 borrowers denied the mortgage product that was widely offered during the country’s housing boom in the mid 2000s and withdrawn for new customers when the financial crisis hit. Additional failings that contributed to Ulster Bank’s larger fine included what the central bank said was a deliberate …