Wasn`t there a restaurant in Covent Garden called " The Pie Factory"? I seem to remember eating Chicken & Leek pies there which only had a pastry top.
On the other hand, my mum made lemon meringue pies which only had a pastry bottom.
Personally, I`d consider anything with a pastry topping a pie. If it`s also got pastry on the bottom, fine.
Poor Mary Berry is getting a lot of stick lately. Can we expect Steak & Kiddly Pie with buffalo steak??