Who knew that the actor Paul McGann has signed the Official Secrets Act? More to the point, who knows why? The Act may be renowned for keeping some pretty trivial things secret, such as the number of Rich Tea biscuits consumed at the MoD, but really, what could McGann of all people possibly know that would place the realm in mortal peril?

All he will say is that he would have to kill us if he tells us and to be quite honest, after an exhaustive examination of his career, that short-cut seems preferable. Indeed, I will happily end it all myself if I read another geek-blog debating whether or not McGann qualifies for the title, 'Longest Serving Doctor'. He is a contender because he was in a one-off Doctor Who film; the only information we can be sure McGann uncovered during filming is the fact that Julia Robert's brother, Eric (playing The Master) cannot act. But then the entire, unfortunate TV audience also uncovered that fact, and I have no recollection of a visit from MI5 – not that I'd be able to mention it if I did.

Perhaps, while playing 'I' in Withnail and I, McGann cracked the conundrum of what the 'E' in Richard E Grant stands for, or even the precise nature of the finest wines available to humanity. Neither seems a clear or present threat to national security, however, which leaves just one possibility.

The single piece of knowledge to which logic suggests McGann is among a tiny elite to be privy, concerns his own family. He and his thespian siblings (Joe, Mark and Stephen) are in fact Britain's secretly-developed defensive weapon against the American Baldwin brothers (Alec, Daniel, William and Stephen).

These two fraternal troupes are the modern equivalent of Snow White's seven fairytale friends; you might well remember the names of two of them, and with the help of blueberries or other memory-enhancing superfoods you might just get the third. But no one in their right mind could ever name all four.

And this, of course, is a cunning test developed by the SIS to identify spies. Anyone able to list the entire quartet would immediately be unmasked as a Soviet sleeper trying that little bit too hard to blend in. I hope that helps.