I researched fuel types and decided that Shell Nitro+ was the appropriate fuel.
The reasons are that it contains approximately 5% additional calorific value, and as it is being converted directly to energy (rather than just 'turning the engine over' and generating heat) then you should get the benefit of that additional energy content.
The other reason is that the data I have obtained show it has a 'maximum' of 5% ethanol ('0 to 5%') and 'trace' methanol. The only other 99 RON fuel, Tesco Momentum, has 5% ethanol and 3% methanol, which is why it has a high octane rating. These components reduce the calorific value of the fuel compared with regular fuel, rather than increasing it in the Nitro+ recipe.
The thing about ethanol and methanol is that they will act as oxidising agents and will react with the metals in your fuel system. Of course, the materials will have been chosen to be as unreactive as possible in the presence of these alcohols, but there will be some reaction. Maybe it is so small as to never make any difference at all, and I suspect that is probably the case, but this stuff may sit in your tank for months.
I'll add I have no great experience to yet go on. Only used 10 litres so far.