Not only has David worked with past Doctors he has also worked with a few past companions as well, in addition to getting to work with Elisabeth Sladen when he was The Doctor!
Sophie Aldred - (Ace, 7th Doctor Companion) 2001 in the Big Finish audio 'Colditz' and soon they will be heard together in the CBBC show Tree Fu Tom .
Nicola Bryant - (Peri, 5th Doctor Companion) 2005 she directed him in the Big Finish audio The Wasting.