Post detection audit and assessment: rates of duty
The duty rate to be applied for kerosene misused as road fuel is the full heavy oil rate. For red diesel the rate to be applied is the full heavy oil rate minus the rebated amount paid on the red diesel. The reason that the full heavy oil rate of duty is used rather than the sulphur-free diesel (SFD) rate is that rebated fuels have previously contained higher levels of sulphur than ULSD / SFD.
This situation is changing however, as rebated fuels increasingly contain lower levels of sulphur, where ULSD or SFD have been marked.
The duty on oil changes on a regular basis following Budget announcements.
You will need to make sure that you build these changes into your assessments.