you can quite happily run the car on Super Unleaded or LRP, these are 97RON which is a lot better than std Unleaded which is 95 RON
Optimax is 98 RON - which is ideal but expensive
BP Ultimate is 97 RON - which is just bloody expensive
and stuff about supermarket petrol being treacle is a load of sh!te.
reason its cheaper is because they can afford to buy more in bulk than your local Shell garage which is simply a franchise, and therefore owned by a person.
its as clean as you get anywhere else, in fact id rather by from supermarkets as at least then you know its not being lying in their tank for 3.5 years.
personally i run my 16v on LRP due to the fact you cant get Optimax in N.Ireland, and LRP is 7p a ltr cheaper than Super Unleaded.
and my car hasnt hasnt skipped a beat since the day i bought it