By Lars Mucklejohn OneSavings Bank has posted a slump in annual profit after the bank took a £181.6m hit from changing customer behaviour. However, the bank softened the blow to investors by announcing a new £50m share buyback. The FTSE 250 bank – which specialises in subsections of the mortgage market like buy-to-let – reported a statutory pretax profit of £374.3m last year, down 30 per cent from £531.5m in 2022. This figure was 28 per cent lower at £426.0m on an underlying basis. The bank’s basic earnings per share fell to 66.1p on a statutory basis from 90.8p in 2022. OSB’s results were dom…