As you might imagine, it's not a question I've given any thought to until now. The Attorney General still has a role to play as the chief law officer of the crown, and I assume the request could be directed to him or her as a member of Parliament. Apart from that, it's something I'd have to consider.
Even if it were directed to us—that is, the public prosecution service—our prosecutor, I assume, unless directed by the Attorney General, would still have to apply the test we've been talking about: is there sufficient evidence to establish a reasonable prospect of conviction, and does the public interest favour the prosecution? That test is applied in every case we do.
But your question is to whom you go at first instance. My off-the-cuff reaction is that the Attorney General could be contacted, but I'd have to think about it.