I've just found on youtube the Christmas episode of 'The Sooty Show' that features Jennie Stallwood (Debbie) and 'John Hasler' in the background. The scene with them in is right at the end of the clip when Matthew Corbett sings his song.
Jennie can be clearly seen a few times during the scene, and once up close, John is more in the background but can be seen a few times especially when he appears at the side throwing paper pieces upwards as in the two images captured below.
One does have to wonder if this was intentional or they were just invited just for fun. Personally I think they were just invited as a treat away from the set of T-Bag.
But I think it is great to see childhood icons be together in a natural fun setting. It really does warm the heart of fans of both shows to see this bit of cross-over material with the kids being their natural selves. ;D