Environmentalists cautioned Britain’s main political parties on Sunday not to water down their climate change promises after a special election result widely seen as a thumbs-down from voters to a tax on polluting cars. The Ultra Low Emission Zone, or ULEZ, charges drivers of older gas and diesel vehicles 12.50 pounds ($16) a day to move around the city. The charge was announced by then-Mayor Boris Johnson, a Conservative, in 2015 and took effect for central London in 2019.