Here is the official line..
Official Secrets Act
UK act of Parliament 1989, prohibiting the disclosure of confidential material from government sources by employees; it remains an absolute offence for a member or former member of the security and intelligence services (or those working closely with them) to disclose information about their work. There is no public-interest defence, and disclosure of information already in the public domain is still a crime. Journalists who repeat disclosures may also be prosecuted.

Posted to avoid tricky situations when the former or serving member decides to decline answering.