His Royal Highness reviewed a selection of cars taking part in the first Brighton to London eco rally on World Environment Day last week.
The rally follows, in reverse, the route of the London to Brighton Veteran Car Run.
Prince Charles took to the wheel of a Ford Focus hydrogen-powered Fuel Cell Vehicle (FCV) and also a Saab 9-3 BioPower.
Organisers say the objective of the rally last week was to bring “tomorrow’s alternative fuel technologies to the capital”.
Ford of Britain chairman Roelant de Waard said: “This rally deepens the understanding of greener motoring – not least among the welcoming party of politicians at Trafalgar Square.”