They travelled in coaches pulled by an 1898-built steam engine, known as Met Locomotive No 1.

BBC: London

The company identified 17 products that met its standard of providing "significant and measurable environmental performance advantages, " including a Lexan film that replaces conventional paint, Harmony water-conserving washing machines, the new fuel-efficient GEnx jet engine and GE's Evolution locomotive, a 208-ton, 4, 400hp workhorse that burns 3% less fuel and puts out 40% less pollution than its immediate predecessor.

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The locomotive is being refitted with vacuum brakes to enable it to tow the steam engine and carriages.

BBC: Steam train to return to London Underground

The engine is the result of an 18-year project to build the locomotive and return it to main line service.

BBC: Loco makes historic main line run