It's a stretch calling ACTA a "studio leftover" since it was just a "bit" that Mike and his co-writers built a song around, rather than an actual leftover song, as some seem to think is was. (I've read a professional review of the first M+M album where the writer assumed that Tony Banks wrote the lyrics to ACTA.)
Well, you incorrectly “stretched” what I meant by “studio leftover”. What you spelled out is what I meant by a studio leftover, i.e., a musical idea that was tried out, but ultimately was not completed. If some kind of rough version had ever been anywhere close to completion, I’m sure that some vestige of it would have found its way to the trading community over the many intervening years.
Yes, the lyrics are interesting to ponder. They do sound a bit Tony-ish, but it wouldn’t be a stretch to think that Mike (with or without further assistance) could have written them too. If they are Tony’s, it would explain why Mike asked Tony and Phil for permission to use the song on the first M&tM album. The original idea for the song was Mike’s in the first place, but if Tony wrote some/most/all of the eventual lyrics, then permission would certainly be needed. (Of course, this begs the question what Phil would have conceivably done with the early development of the idea to require permission being asked, unless that was just a courtesy since they were returning to an “all titles done by all” position.)