Westminster Council now operates an emissions-based charging scheme. The price to pay will be adjusted based on the CO2 output and fuel type of your vehicle, see https://www.westminster.gov.uk/parking/parking-prices for details 

You will be quoted the adjusted charge before you commit to pay. EV/PHEV drivers - the 10 mins/max stay concession no longer applies. You must now purchase the full duration of your parking session. 

For more information please see the following: https://www.westminster.gov.uk/parking/changes-how-we-charge-parking