Well a little bit concerning.
My insurance company when I asked about changing my reversing light from bulb to MOT put me on hold whilst they contacted the underwriters. Underwriters came back with reversing light is OK because their are basically no restrictive laws for these but for all other units the are homologated for either bulb, HID or LED use and one can legally only replace the complete unit and take care of any self levelling and cleaning functions required (over 2000 lumens). All such changes need to be *accepted* and recorded on the policy to be covered by your insurance as do all vehicle alterations.
As for LEDs not failing an MOT they can, especially on DRLs. DRLs are MOT tested to correctly operate in conjunction with headlamps. Proper DRLs should dim when headlamps are turned on. Some P21W LED replacements can not operate correctly with voltages below 12V. Some won't illuminate at all and others will flicker.
This is not a case of the LED / modifications police. Anybody can do what the hell they like but don't expect insurance companies to pay out. They are perfectly entitled to not pay out / cover you if you have not disclosed relevant facts (e.g. modifications) to them and certainly so if that modification was a factor in the accident (eg. dazzling someone) or theft (boy racer liked you Recaro racing seat and full harness set-up).
I can assure you they WILL protect their interests and wriggle like mad come a claim time. Not only could you be seriously out of pocket (for the rest of your life if a lifelong incapacitation or death is involved), you will be prosecuted by the real police for driving without valid insurance.
You choice, not mine.