Some of HSBC's largest shareholders are pressing for the bank to reconsider the costs of being domiciled in the UK, according to a report.That follows a promise repeated on Tuesday by Labour's Ed Balls to raise an extra £800m through an additional Bank Levy, which would come on top of the increase already announced by the Prime Minister in last month's Budget.For one investor, who asked not to be named, the increased burden from taxation meant the case was becoming "unanswerable" for HSBC to conduct a further formal review of the location of its headquarters, Sky's Mark Kleinman reported on Tuesday.