The UK's largest banks are heading for further losses in high street operations as impairment charges and the issue of bad loans continues to worsen, accountants have warned. KPMG's report UK Banks Performing Benchmark Survey reveals that the 'foreseeable future' will be a period of strain for the banks' retail businesses, as they continue to suffer from high levels of loan impairments. The report said that: 'On the UK retail business, for the 2009 half year, all the four banks reported decreased profits when compared to the 2008 half year.' 'Retail banking is still just profitable at lower levels, but with rising impairments it seems probable that it will fall into loss-making in the second half of this year.' HSBC and Barclays have reported an increase in profit margins, but Lloyds and RBS are continuing to suffer, the firm said. KPMG said that investment banking profits are unlikely to be sustained as the income made from selling and trading bonds and loans declines, but it predicted that improvement could come 'over the next two years' as banks begin to charge more for lending.