In the 2000s, ITV created new end-credit sequences for repeat showings of many of their successful programmes of previous years, including Inspector Morse (1987). In the new credits at the end of The Dead of Jericho, they have erroneously credited James Laurenson with the part of Colin, in addition to the Richards brother whom he did actually play.
It turns out that Ned Turner wrote the "blackmail" letter ... but George Jackson referred to it in his phone call, and there is no way he could have known about it. No, this isn't right. Richards refers to it when he calls him and Jackson just follows along. Richard a assumes the person calling is following up about the letter, but Jackson is calling on is own behalf to blackmail him, as he knows about him from all his spying.
As Morse enters Richards' office, you can see the mic top left centre of the screen.