I am British and living in London. From the article:
"London saw wild scenes of a weekend mass exodus before the start of a Christmas lockdown and travel ban sparked by a new, more infectious mutation of COVID-19."
I saw plenty of pictures shared by families meeting in London on Christmas Day so perhaps the OP should have put “this is a consequence of people breaking the restrictions on Christmas Day” caused by wilfully ignoring the rules or confusion.
The mass travel before the Boxing Day restrictions kind of proves people were away from home, seeing family etc this spreading the virus.