Westminster have actually said they're treating it as normal Sunday restrictions. Can't see that Ealing have said either way...
https://www.westminster.gov.uk/bank-holiday-parking-controls
Actually, read down on your link...
Bank holidays
The control on the residents’ parking spaces does not apply on Christmas Day, Good Friday, or on official bank holidays.
It doesn't mention specifically mention Boxing Day, and according to .gov.uk Boxing day isn't an official bank holiday...
Hmmmm that is going to be an interesting one for enforcement. You are correct, Boxing Day is just a normal Saturday and not officially a Bank Holiday...28th is the substitute day. But is the very notion of Boxing Day still a bank holiday in principle even at a weekend? I got a feeling the...