In the radio plays, she's performed by Anna Chancellor, and shows up as Head!Ann frequently in Smiley's thoughts, when she argues with him, teases or encourages him, and provides part of his inner voice.

I like that immensely as both a writing and a casting choice, even if Ann always will look like Siân Phillips to me. I've always loved her mention in The Secret Pilgrim, so I appreciate the step further of having her tell one of its stories.