HSBC has joined other banks in warning it could leave the UK if the Commission on Banking recommends the break-up of the country's major banks.In much more explicit comments than its rivals, Stuart Gulliver, the head of HSBC's investment banking business and a possible future chief executive of the bank, told a conference yesterday it could leave London if ordered to split its investment bank from its retail lending operations.Gulliver said a recommendation by the commission to break up the banks would have "significant implications clearly for where we may choose to headquarter our institution."Barclays and Standard Chartered suggested last month they could relocate to Asia or the US if the coalition government-appointed commission did recommend a separation of activities.HSBC has already laid some of the groundwork if it did decide to move. It shifted it chief executive's office to Hong Kong at the start of the year, though has consistently denied this is a precursor to a shift of domicile. "I want to be crystal clear. Our preference is to be headquartered in the UK," Gulliver told the conference in London."So we would hope there isn't a conclusion that causes the banks that actually didn't take any money from any government anywhere in the world to have to move their headquarters. It would be very very regrettable."