You'd be very unlucky to find a cop that knows anything about HID on bikes, and is willing to prosecute you.
I don't even think VOSA would do anything about it at stop check sites, and they're the superpower when it comes to Vehicles.
Having checked the question of HID's on bikes out at work (I am a Traffic Police officer) I can tell you they are definitely NOT legal, unless they have the self-levelling suspension and headlamp cleaning system.
The penalty that we could deal with you for is basically a £50 fine and no points. You could get a defect rectification notice too, but that would just require you to put it back to standard. You're unlikely to get done by VOSA as the chances of them working at night are about nil, and obviously you wouldn't be using your bike at night if asked
.
The big problem, and the reason I would never do it is the insurance issue. Lights are a safety item and if it can be shown that lights were a factor, however small, in a collision then you're going to have problems.
For instance: You're in a national speed limit at dusk going round a left hand bend in a spirited fashion and your correct position would be near the centre line. White van man coming the other way is cheating over the centre line cos his van really isn't a touring car that can hold a line through the bend. It's not going to end well for you. When we get there to investigate he says he was dazzled by your lights and/or it's a serious injury and we'll take your bike away to be examined.
Regardless of what happens to WVM you could get done for dangerous driving (because you made a modification to your bike that made it illegal) and it will massively affect your insurance payout.