The law is quite clear.
Vehicle Lighting Regulations clearly state that obligatory vehicle lights need an APPROVAL mark
Approval marks are under the Designation of Approval Marks Act which says anything approved under the UNECE regulations is legal in the UK
The Road Traffic Act states it is an offence to supply, fit or use a defective item on a motor vehicle.
Construction and Use regulations does not mention vehicle lighting so in this context is irrelevant.
CE stands for European Conformity which basically means that the product is free of harmful substances such as arsenic/lead etc so not really applicable to LED headlights.
E marked? E + number in a circle is a country code. It is NOT an approval mark.
DOT/DOT approved = Department of Transport (USA)/Department of Transport does NOT approve anything as it is a regulatory body not an approval body. DOT regulations are not applicable in the UK it is a USA/North and Central America regulations. Some of the DOT regulations may or may not be compatible with European regulations.
Vehicle lighting Regulations can be found
here schedule 4 and 5 apply to headlights
UNECE regulation 48 is a summary of vehicle lighting regulations and gives a broad outline to all vehicle obligatory lights and references the applicable regulations for individual lights such as R112 for headlights R 23 for reversing lights, R 10 for electromagnetic compatibility etc. UNECE stands for United Commission Economic Commission for Europe and is the basis for vehicle harmonisation regulations in Europe
As for the MOT it is a basic safety check and does not check the legality of the lights but on their functionality. The EU annual roadworthiness test is a directive (so not legally binding) says the lights markings should be checked for compliance but this word was missed out on the latest MOT which come into force this year. EU directive
here section 4.1.4 compare that with the MOT
section 4.1.4
Most if not all cheap LED headlights are not approved for use in the UK as they do not have the correct approval markings on. If headlights are marked DOT, SAE E + number in a circle then no matter what any trader says they are not road legal in the UK.
Now it is quite feasible to fit illegal lights and get away with it, just like it is possible to get away with breaking the speed limit/drink driving etc. There again you run the risk of getting caught.
Now your motor insurance policy will require you to declare any modifications to your vehicle. Now your motor insurance policy will require you to keep your motor vehicle road legal etc. Try telling your motor insurance company that you have carried out an illegal modification to your vehicle and see what they say in the event of a claim!
Brendan