Quiz: What's The Connection?

Today I was watching an adaptation of Agatha Christie's The Blue Train Mystery which stars her brilliant detective Hercule Poirot. I enjoy the newer adaptations of her novels especially because they feature many British actors who can be seen in several period films.

There were three period actors who I recognized and I was wondering if anyone else could find the connection I did.

Nicholas Farrell


Lindsey Duncan


James D'Arcy

What connection do these three actors share? I'll post the answer after a while if I have any responses.

Hint: Besides being in The Blue Train Mystery I don't think they've been in anything else together. And think period films! :)

Any guesses?