BRL - I am also familiar with Pippin, his owner and their airbourne adventures (due to my 4 year old daughter - honest).
I have only noticed the same aircraft in all the episodes that I have seen - a Slingsby Firefly. I too am quite charmed by the paintscheme.
No idea where it is based. Do you think that is really Auntie Mable and Pippin in left & right seats?
Mr. W