They are gaining one! Swiss banking privacy rules down under EU pressure. The UK now have freedom to keep large money more private than Swiss can do from now.
That's exactly opposite of what the United States has been pushing for the last couple of decades in terms of banking secrecy, pretty successfully. The U.K. could alienate the US government right now, but I bet they won't.
Switzerland already bent its traditional legislation to comply with new EU ruling about banks secrets snd reporting. The UK banking just got its chance.
Switzerland did that because the alternative was, concretely, losing the ability to keep foreign customers, so they chose the lesser evil.
Why do you think it would be different for the UK?