Haven't seen that in years... ISTR PTerry is in a couple of the Discworld adaptations, and of course Stephen King has a secondary career out of cameoing in all the adaptations of his... DW-wise the only ones that spring to mind are Terrance in The Silurians, and you can hear RTD as one of the "are you my mummy" voices in hospital in the Empty Child/Doctor Dances cliffhanger. Oh, and the guy wrote The Space Museum is in Sontaran Experiment, cos he was an actor before he was a scriptwriter, even though he wrote for DW before appearing in it. Similar for Toby Whithouse in Twice Upon A Time, and of course Gatiss, who was an actor/comedian first.
It's a "blink and you miss it" in-joke. You briefly see a cover to, IIRC, Time magazine, and it depicts Clarke as the American president and Stanley Kubrick as the Soviet premier, relating to the geopolitical tensions in the 2010 film. Ironically, a friend posted a video on Facebook a few days ago about how everyone's forgotten that 2010 exists, and here I am, posting obscure 2010 trivia.