What petrol should I use in my Audi A1?

I recently purchased a 2017 Audi A1 998 cc from a reputable family garage where the owner has a great reputation for buying and selling to local people. He advised that I should use higher octane petrol...

Do I need to use high octane fuel in my Porsche?

Can you advise, my Porsche has 98 octane fuel printed on the filler cap. This is not always available and I use 95 Octane without any discernible effect, then filling the tank with 99 octane now and again...