I'd just be a little wary of chucking in a Chinese HID replacement setup in place of the standard bulbs. The stuff on Fleabay will most always be the cheapest Chinese sh*te...
Technically, it's illegal to change the light source under construction and use laws, given that the reflector is designed for one type of light and should be different for a HID.
However, there's no specific MOT test yet - as long as it's aimed properly and has a legal beam pattern, they shouldn't fail. Plod could still stop you if you're dazzling (which is likely given the pitching on a bike versus a car) and get antsy. They have been getting brutal with chav-hatches over the past couple of years and it's your luck whether you get a copper that would slam you in the same bracket.
I've personally never had an issue with the output of the standard lights, but your call - information above is just for you to make an informed decision.