The last few days / week ive started to notice my MPG decrease.

The only thing ive done to the car is put my 18s on (wondering if its my right foot going down more to accelerate). but is needing a service as the indicator has come on

My average MPG used to be around 43 but now it gets about 33 if im lucky.

Car is a mk5 1.6 (105bhp)