Is MI5 protecting HSBC?

Recently Private Eye magazine made a Freedom of Information Act request to a government department concerning Lord Green, ex chair of HSBC Group. ( I no longer have a copy of the article and cannot recall the name of the department). The exemption in the Act which the department used to justify their refusal to comply, only applies to the security services, which suggests that MI5 is in some way involved with Stephen Green. I wonder if they are also protecting his old bank, HSBC. Here is the exemption referred to: