This is based on S1e2 ( Een fatale vergissing - A Fatal Mistake) of the Belgian version of the show with the same name.
The English flag is rarely seen in UK number plates but Scottish and Welsh flags are quite common in their homelands.
When Professor T is talking to Claudine Froggatt and he imagines dancers dancing the can-can, they are holding letters which collectively spell INFIDELITY.
Emma Naomi and Ben Miller both appeared in 3 installments of the first series of Bridgerton (Miller appeared in 8 installments).
The number plate on Jonathan Fell's car (EU 72 WXI) could be a Brexit reference. The UK were accepted into the Common Market in 1973 and stayed for 48 years. W is letter 23 of the alphabet, X is letter 24. If I stands for a one then the three letters added together make a total of 48.