My thinking on the mileage vs fuel consumption is as follows:

Lets say mileage since last reset of trip computer was 2,000kms and it used 400 litres of gas then the fuel mileage would be calculated at 20litres per 100km. Now imagine you were to roll back the mileage by 1,000kms. The computer could possibly now think it has used the same 400litres to drive 1,000kms and thus the fuel mileage calculated would be 40litres per 100kms. Now imagine this on a grander scale mileage wise and hopefully you will see whta I am getting at.

If it is the case that it is unlikely the mileage has been tampered with how can you explain those outrageous fuel consumption figures on the trip computer. Has anyone else experienced this ?