Quoting myself but a bit west of Stamford bridge and pay & display is free on Boxing Day.
Also parking in zone S around Fulham Rd in Hammermsith & Fulham council is free on Bank Holidays:
https://www.lbhf.gov.uk/parking/pay-and-display/bank-holiday-parking
Kensington & Chelsea pay & display is free on Boxing Day which sort of indicates they don't have wardens out that day
https://www.rbkc.gov.uk/parking-transport-and-streets/parking-permits/visitor-parking-and-pay-and-display
That is to west of Stamford Bridge near Chelsea and Westminster...