Mystery "train music" in "A Hard Day's Night" - Ringo doesn't have a clue

The subject of much online debate in Beatles circles over the past week or two has been the identity of the group heard performing over Ringo's transistor radio early on in the "A Hard Day's Night" film.

As you recall, Ringo switches on his radio and starts grooving, much to the annoyance of the uptight establishment gentleman the band ends up sharing a cabin with.

The music is fairly generic, by-the-numbers instrumental rock and it's been debated for years whether it's performed by the Beatles -- making this an otherwise unreleased rarity -- or some other group.

As recounted by Beatles Examiner, Chris Carter, the host of Breakfast with the Beatles radio show, recently aired the full version of the track and is of the mind that it's the Fabs:
“I think it's 'them' for the following reasons: It sounds like them. The tape box said 'The Beatles.' If it was another group, that other group would have claimed it was them sometime in the last 50 years! It was found along with other music not used in the film by George Martin.”
Others aren't so sure. Including, it turns out, Ringo himself. Asked about the song this week, he said:

“I'm afraid I have to help keep it a mystery. I don't remember.”
You can hear the music in the video below, about four minutes in: