Ely to King's Cross, since the May timetable changes.
The direct Great Northern Ely to King's Cross trains wait at Cambridge for so long that for most hours in the day, instead of boarding the xx:47 departure at Ely, you can board the following CrossCountry train at xx:53, and still meet the official connection times to be able to change back onto the Great Northern train at Cambridge. This one is amusing because the train you're catching up with is actually a fast train, not a stopper, although it's fair to say that the "fast" in this case only refers to the part of its journey after it has left Cambridge.
The direct Great Northern Ely to King's Cross trains wait at Cambridge for so long that for most hours in the day, instead of boarding the xx:47 departure at Ely, you can board the following CrossCountry train at xx:53, and still meet the official connection times to be able to change back onto the Great Northern train at Cambridge. This one is amusing because the train you're catching up with is actually a fast train, not a stopper, although it's fair to say that the "fast" in this case only refers to the part of its journey after it has left Cambridge.