No you’ve got it the wrong way round the Intercity 125 was an impressive feat of engineering designed very quickly as a temporary stopgap while lines were elect

No you’ve got it the wrong way round the Intercity 125 was an impressive feat of engineering designed very quickly as a temporary stopgap while lines were electrified and still holds the record for world’s fastest diesel train. It was a side project of the engineers that were designing the Advanced Passenger Train that was being developed at the time, which was supposed to be able to run at up to 150mph on conventional routes using tilting technology. The intercity 125 incorporated a lot of the lightweight construction research that was done for APT. Not much was done to the track to enable higher speed running, some resignalling and very very occasional route realignment for higher speeds. The intercity 125 achieved better times by being more lightweight and having faster acceleration than conventional locomotive hauled trains of the time, but it was only 15mph faster than the conventional trains. Most of Western Europe has standard lines with up to 125mph running, it is not uncommon. E.g a lot of the old non-tgv line between Paris and Bordeaux supports trains running at up to 200kph (125mph) Likewise 200kph running is common in Germany with conventional trains. The track in the UK was not special, quite the opposite as when the 125 was introduced we still had a lot of victorian style jointed rails that had been obsolete since the 1950’s. Britain was slow to upgrade to continuous welded rail, it wasn’t gone from all main lines until the 1990’s.