A concrete pillar wobbles when Reegan is thrown against it.
As the alien in the spacesuit on the steps flails backwards, the actor runs who runs in trips and hits the left hand brick wall, which bends and rattles revealing it to be plywood.
Just after Liz Shaw confirms the radiation figures (around 12m 33s), the Doctor refers to 'Carrington' as 'Clarrington'.
During his meeting with the Doctor, Liz and the Brigadier, a boom microphone shadow falls across Carrington's head.