>>1549212>this will make you chuckle but the reason is the loading gauge is so tight. frog and kraut trains literally won't fit under some of the bridges and tunnels, even though they can theoretically run through the channel tunnel right up to the top of scotland as far as track gauge is concerned.Yeah... no.
While British Loading Gauge is tiny af, the Channel Tunnel and the Channel Tunnel Rail Link (aka High Speed 1) are built to a continental loading gauge standard. This is why the British Rail Class 373 has extending steps - it is built to British Loading Gauge standards, as the train ran on regular Network Rail tracks from London Waterloo to the Channel Tunnel. It could also be used for "North of London" service.
When the CTRL was built and service moved to St. Pancras International, the Class 373 had to use its extending steps at all the stations it served at in the UK.
This was why Eurostar started replacing the 373 with the Class 374, which is a Siemens Velaro e320 (specification for the Eurotunnel). This Class 374 uses Continental Loading Gauge, meaning it will be limited to running on only the CTRL and London St. Pancras, as it too big to fit on any other British rail lines.
It's worth mentioning that High Speed 2 will be built to Continental Loading gauge, however with the cancellation of the HS1-HS2 Link, it won't be possible to run the 374 directly onto HS2.
