The British Rail Class 373 or TGV TMST train is an electric multiple unit that operates Eurostar's inter-city high-speed rail service between England, France and Belgium via the Channel Tunnel. Part of the TGV family, it has a smaller cross-section to fit the smaller loading gauge in England, it was originally able to operate on the UK third rail network, and it has extensive fireproofing in case of fire in the tunnel. It is both the longest——and fastest train in regular UK passenger service, operating at speeds of up to .