Yea my consumption is proper sh1t too mate. I struggle to hit 30mpg too, i average about 28mpg.
A spark plug change service usually helps, and if you are hitting 40-50k on original sparkys that could be the problem, ive always noticed a differance on economy after an overdue service-plug change.
As for 99 octane, in tests it has been shown that that it takes a good few refuels for the car to adapt and show any mpg or performance gains from the fuel round about 8-10 refuels.