Why does a car need side repeaters?

a car in Europe needs indicator side repeaters to meet with a law called "Construction and use regulations" which specifies what can and cannot be fitted to a vehicle and where it can be fitted. this regulation states that indicators need to be seen from the side which is why when cars are imported from the US or Asia they need to have modifications to make them legal to use in the UK, ie have repeater lamps fitted. taken to extremes it means that vehicles like a lotus convertible has a tiny screen fitted between the seats, this serves no purpose but Construction and use regs state that this type of vehicle needs a rear screen. robb