Just another little update. Since getting the car back I've only been doing relatively gentle local runs, including ferrying a disabled passenger so no pushing the boundaries.
That said, it's been driving very smoothly, which it hadn't been for some time, so I suspect the old F125 had been upsetting/misleading the TCU for ages whilst not quite triggering limp mode.
But today I had the opportunity of a near 100-mile round trip mainly on quiet country roads. All working very much as it should now.
A little lesson here: If you think the gearbox is behaving a bit oddly cast a glance at the DIS and see if the selected gearstick position is highlighted clearly. If it's not, or is flickering, that may all be down to a failing F125.
