"Oh, I say!" - Harry delivers one of the best ever ‘first entering the TARDIS’ reactions in the history of Doctor Who.
Robot - Season 12 - 1974/5
Also; love the way the Doctor indignantly snatches back Harry’s half-eaten Jelly Baby and throws it back into the bag! Harry does not believe in the TARDIS, therefore Harry does not deserve a Jelly baby!
Also also; love Sarah Jane’s face as she eavesdrops at the TARDIS door.