Never been stopped but I had thought this covered it (from the NTTA):
Marking of rear overhang
Between 1m and 2m, ensure the end is clearly visible by attaching a piece of cloth or similar.
Between 2m and 3.05m, a marker board as defined in the Regulations must be fitted and illuminated at night.
.... but now I have also found this !?!?
The lighting board must be wide enough so the outer edge of the rear lights is within 150mm of the outer edge of the boat. This lighting board should be positioned within 1 metre of the end of the total overhang (which is often the mast), or otherwise the end of the overhang would have to be lit with an addition reflector and red lamp. The lighting board should not be more than 1.5 metres off the ground. The trailer also requires at least two amber reflectors down each side.
The overhang, with engine in tilt position is 1.6m though the transom is
I did originally mount the lights/brackets on the end of the sliding bars that were part of the original lighting board so I could slide in and out - but changed them to fixed mount as it removed all vibration and stopped me having to replace blown bulbs as often.
The good news is I have back up lighting and haven't had an issue with lights-out which would cause our friends in blue to stop me >>>
ANy experts out there .... pls