I think this is his daily vaccine progress update.
The Torygraph says: "The Armed Forces involvement will be spelt out in greater detail at a Downing Street Press Conference at 5pm as Brigadier Phil Prosser, the military lead on vaccines, is due to appear alongside the Prime Minister and Sir Simon Stevens, chief executive of NHS England".
Whenever I hear of a brigadier doing a press conference alongside the Prime Minister I immediately think of some of the old Dr Who episodes.