I think that there is red petrol (tax wise) but it is not red! It is called Aviation Spirit (you don't expect those toffs at the flying club to pay tax do you?) Aviation Spirit is as far as I know a very low grade of petrol similar to 2 star ULP as years ago it was notorious for burning out valve seats in spivs motor cars. It is a bit much when people using cement mixers or chainsaws have to pay lots of tax whilst fliers get off scot free. Incidentally aircraft piston engines tend to be large capacity low compression jobs timewarped in the 1950s but the fuel they use should be OK for 2 strokes and industrial engines.
By the way, I did hear of a toff with a private jet that flew beautifully on kerosene or central heating oil. It was just a case of tweaking the gas turbine to run on whatever was cheapest! When I hear that modern fighter jets using afterburners get through about six gallons a second it makes me puke. (they aren't paying 95p/litre are they?)
Aviation petrol is very high octane and is known as Avgas in the military. When I was in the FAA it was fuel for Fairchild Hillers, and the army Bell "Sioux" .
Aviation jet fuel is either Avcat, Avtur or Avtag - depending on temperature - although naval Wasp helos could also use diesel.
Aviation starting fuel in days gone by was Avpin - used on an early type of Wessex helo.
Trouble is, it is not just boats. The moment the Government introduced "red petrol" two things would happen. Firstly there would be thousands of people using it illegally in cars. Secondly there would be a huge legal demand for it for use in lawnmowers, garden tractors, petrol generators and other small petrol appliances. That legal use would probably cost the Government even more than the loss of road fuel duty for boat use.