This last item is bit of self-indulgent fun, finally signing off my long campaign to counter DfT's claim that distributed traction would give the Intercity Express Train in diesel mode magical powers, allowing it to outperform the more powerful IC125s it was replacing.

When Class 800 bi-modes were ordered for services north of Edinburgh I queried their performance over the northern climbs. I was reassured that distributed traction would offset the power disadvantage compared with IC125.

This clearly contravened the laws of physics. My brother the Prof even ran a model which demonstrated that, while the IEP zipped away because of its weird DfT specified acceleration curve, once the initial sprint ran out of power the IC125 caught up and disappeared into the distance.

But who believes in abstruse calculations? However, eventually, LNER's December 2019 timetable meant that we were able to test the validity of Newtonian physics by comparing a nine car Class 800 against IC125 performance over the southbound climb from Inverness to Slochd Summit. I am indebted to my chum David Shirres for the details.

The climb starts at Tomatin, which the Class 800 passed at 70.3 mile/h. After 3.5 miles at a gradient of 1:60, the speed at the summit was down to 55.3 mile/h. This compares with 65 mile/h for a 2+9 IC125.

Which is as expected, since the IC125 has a power to weight ratio of around 10 hp/tonne compared with 8.6 hp/tonne for a nine car Class 800 with its engines derated for reliability.

Just to emphasis the point that power to weight is the determinant, ScotRail's Inter7City shortened IC125s touch the 75 mile/h line speed limit before braking for the 50mile/h restriction after the summit.

Does it matter that 2 min are lost on the climb to Slochd summit so early in the journey? Not really.

But this real-life comparison is a reminder that when it comes to traction performance the cold numbers, not wishful thinking, should rule.