After some talks with other people I have almost discarded that the mystery version of The Ides Of March was recorded on the Metal For Muthas session. Now, taking into consideration what you are saying @Forostar , let me say this. We know that Burning Ambition (B-Side for Running Free single) and Running Free (from Axe Attack album) come from a recording session Maiden did with Gary Edwards (November 25 & 26, 1979) Lineup: Di'Anno, Harris, Murray and Sampson, nothing else, that I know of, was recorded then or has not come to light, which means that the mystery version could come from this session.@Luisma @srfc @Magnus
From album page on wiki:
Before the sessions with Malone, the band made two attempts in December 1979 with two different producers while still a four-piece. Guy Edwards, the first, was dismissed as the band were unhappy with the "muddy" quality in his production, while Andy Scott was sacked after insisting that Harris play his bass with a pick rather than his fingers.
So if that is correct, Maiden was in the studio three times after Muthas&BBC and before the appearance of the studio version! Still think it is the album session, if we believe Clive is on it. He never played in Maiden with a four piece. That was Sampson.
The sessions with Andy Scott (December 1979 (does anybody know for sure the dates for this sessions?) ended up being a complete waste of time in which they only tried to improve some recordings they already had (Running Free) because they wanted to make the drums sound better.
"Oh yeah, a long time ago. Well, the first thing that was, I suppose fairly successful, was a thing called 'Running Free'. And they had a demo of it with the original drummer. And Clive Burr had just joined the group and it was only Paul Di'Anno's 2nd song or something. So they came to me with an idea of just re-recording the drums, cause the drums didn't sound very good." (Andy Scott interview – The Iron Maiden Scandinavia FC Webpage - 1991)
To my knowledge nothing came out of it, but the mystery version could have been recorded or re-recorded with Clive on this sessions.
As you pointed out, the bootleg from Wakefield Unity Hall, February 7, 1980, has the mystery version played as an intro tape.
Maiden recorded their debut album, according to my research between February 13 – 29, 1980, so the mystery version of The Ides Of March could come either from the sessions made with Gary Edwards or is the only thing that survived from the Andy Scott sessions.