Who?!?!?
It's probably not going to be productive to start randomly adding "John" in front of various surnames. Read back through all the clues, and add this one:
One of the earlier incorrect suggestions was Percy Thrower... He, however, did once discuss the name we are looking for in an episode of Blue Peter. It's difficult for me to give any more detailed clues without actually giving the answer away. Now, I checked before posting the question to make sure it couldn't just be Googled by looking up the "grandfather, father and son" bit, but it's not impossible to find out the answer by doing a bit of research...