From their maximum speed of 125 mph.
125 (plural 125s)
- (UK, rail transport) A high-speed train (HST) powered by two British Rail Class 43s, one at each end.
1999 June 16, Hoppy, “Re: HST from Paddington”, in uk.railway[1] (Usenet):How much rail horsepower does a 125 have? Well I don't have the actual TE curve on me here (it's at home) but I can approximate.
2003 December 1, Sean Marshall, “Re: Voyager/Meridian differences”, in uk.railway[2] (Usenet):Most of the cheap tickets are valid on both 125s and Turbos - indeed some are ONLY available on 125s (eg First Plus London Day Out).
2010 January 6, McKevvy, “Re: Could you safely lie between the rails of an HSL?”, in uk.railway[3] (Usenet):When I was an apprentice many years ago, the 125 used to come through Markinch station in Fife at 1.27pm every weekday.