Philippa (Pip for short) and Emma make up a British Rail High Speed Train InterCity 125 set. Their first appearance was in "Gordon the High-Speed Engine", where Gordon was taking a railtour to Carlisle, so they took back the Express for him.
- Their names happen to be the names of two siblings in the Agatha Christie novel, A Murder is Announced.
- Thomas and His Friends was the only time in which Pip spoke. Until then, Emma only spoke.