I may be wrong here, but I understood that the plan was to progressively electrify north of Bedford, with London - Bedford stage 1, then on to Leicester “and beyind….”. This was a London Midland Region plan, and based on the APT plan for the WCML which would have released loads of AC Locos and hauled stock that needed a home, and where better than ‘next door’.
However the troubles with the APT, and then sectorisarion in ‘82 effectively scuppered that, with Intercity (quite rightly) deciding that if there was to be more ‘intercity’ main line electrification, then the ECML was the best place to do so as it offered more revenue gain and cost savings than the MML, and therefore a better return on the investment.
Lodged in my brain somewhere is that there was a submission for at least part of the MML electrification in to the DfT (or ready to go into the DfT) around 81 / 82, which was subsequently withdrawn. The ASLEF strikes around then didn‘t help obviously.
Certainly nothing was authorised for the MML, but I thought initial design work had been done. Certainly when Leicester was resignalled in the mid 80s it was done with full electrification clearances on all the gantries and immunised track corcuits etc., so someone thought it was in the offing.