Stiknruda
I am a commercial pilot and flight instructor. This pilot was not in any urgent or emergency situation. The weather was beautifully clear, with light turbulence. There was no conceivable reason for being over a very crowded area of sea at below 250'!
He put himself in a situation that endangered at least 20 vessels in the bay and my aircraft, which had priority hence my assumption that he failed to see me. He then climbed to cross the Needles and descended the other side to about 100', although by then complying with Rule 5 being away from vessels until he raced a speed boat. Although I admit I cannot accurately judge his height for that one it seemed extremely low, and on previous behaviour we can assume he was still at 100' without risking doing him much injustice.
If anyone does suggest I misread my altitude, I renewed my IR the day before, and do not misread altimeters, and was specifically noting the altitude both on the altimeter and by judgement with the land (I know the Needles area extremely well, having over 500 hours instructional experience from Bournemouth) to keep myself both safe and legal.