Is the curvature bad enough on the MV that a new line would be required? A small laser-targeted intervention around Ridgmont might have helped, but junction 13 of the M1 makes that more complicated, unfortunately. The line from the MV's MML crossing down to Millbrook is really straight as-is though, with gentle curves through Lidlington, so I don't think a new line would wash its face. Perhaps a larger deviation around the north side of Ridgmont/Brogborough could suffice, if required (though it would cost you the stations at Apsley Guise and Ridgmont). That should give a much straighter route, abet I suspect the railway was built where it was for a reason (and I don't have a topographical map to hand!)