On page 65 under (f) Fuel provided for private use, you mentioned the benefit is equal to 18,800 multiplied by the percentage.
This threshold actually FA 2011 and FA 2012 it is 20,200
If you review Example 5 on the same page and the answer on page 187 it will be clear as the used number was correct (20,200), and it is mentioned also on rates sheet on the beginning of the notes also.