I used the REDEX advanced petrol cleaner when i first got my motor. £14.99 from Halfrauds
Put it in half a tank full, then run it down to nearly empty then refilled. Then repeated a couple of tankfull's later. Seemed to do something, but wasn't expecting miracles. Will stick some more in soon.....
I always fill up with Tesco 99RON, Shell V-power or BP ultimate.