Yeah, I thought Tornado was held back by lack of water troughs as well as the 75mph limit that Network Rail impose on steam locos (its obvious she can easily top 90mph), as well as not being given priority up the ECML.
However, do bear in mind that the challenge was to pit the fastest modes of transport in 1949 against each other, and the roads in 1949 were a good deal emptier in the UK than they are now. I suspect the car would still have won.
Paul