“31. Where all or part of the work on a case is done in a different location from that of the solicitor’s office on the court record, the appropriate hourly rate for that part should reflect the rates allowed for work in that location, whether that rate is lower or higher (provided that, if a higher rate is claimed, a decision to instruct solicitors in that location would have been reasonable). The location of a fee earner doing the work is determined by reference to the office to which s/he is, or is predominantly, attached.”