I'd agree the current UK regulations are hopelessly out of date, but IMO that's not a valid reason to knowingly break the law. I'd also agree it would be enormously helpful if the law were changed so that reputable lighting manufacturers could more easily offer properly certified LED replacements, and car manufacturers could properly integrate them into the design of the vehicle. The latter is needed because the power saving benefits of LED technology will be lost if you need to fit resistors to make them work properly. I'm sure it's only a question of time before all this happens.
Current uk regulations are out of date which is why new cars in the uk are tested against EU type approval standards, in the eu standards you will find all the new technologies and the provisions for them that allow LEDs and new LED head lights HIDs (which aren't covered in uk law) and even the new laser headlights. Modern lights spin twirl and do all sorts of fancy tricks like selectively blocking the light in the direction of oncoming cars, my new car has auto main beams.
Non of this stuff is covered in uk law and is allowed under EU law which is why this isn't a black and white case and even our own government don't really know where things stand. Essentially if the bulb and the light is e marked (and you can buy e marked LEDs) then the law is happy.... Unless they want a battle through eu courts!
If your bulb and lens are e marked and you inform your insurance co then they will be happy. Insurance companies do not check every component is appropriately marked or check the validity of the marks. In fact the insurance company very rarely sees the car. If you have informed them and they have allowed it then it's not a problem.
The Philips bulbs are tested in a certain range of cars, Philips are not about to test every car made in the last 20 years to ensure compatibility. But as mentioned if the bulb had the mark then it is deemed suitable for any e marked lamp (those tests are for American SAE standards.)
This whole argument and the reason we are having the discussion is because of one arrogant member basically says "I could fix your problem, it's very simple but I'm not going to because ethics prevents me from doing so" which is just plain rude and obnoxious, if you don't want to comment, don't comment. The laws he's quoting don't even cover the situation and you're defending him without any more knowledge than just happening to agree with him. It's the whole reason the the forum member had left and the thread is getting criticised.
The argument for LEDs is that they last longer and provide a better quality of light, usually whiter for better visibility, which can be seen easier and travel further without the need for reflectors. They respond quicker making them better for brake lights and they are less susceptible to the environment and vibration.