Recently, US President Joe Biden attended the G7 summit in the UK. Various videos (e.g. here) show his motorcade. As might be expected, many of the vehicles are fitted with (and using) the red and blue emergency lights that are standard in the US.
The Road Vehicle Lighting Regulations (1989), section 11(1), stipulates that "No vehicle shall be fitted with a lamp which is capable of showing a red light to the front, except [cases that are not relevant here]". It would seem clear that the president's vehicles are contravening this.
Did the UK government take any action ahead of the visit (e.g. special regulations) to authorise this use? Alternatively, do principles of diplomatic immunity enable the president to disregard such regulations? Or is there simply a pragmatic decision to ignore the issue?
Put another way: if an overly-keen traffic cop tried to take enforcement action here, how would it end?