There is no logical reason why a flying instructor flying his employer's aircraft and deriving pleasure from his instructional flights should not be charged a benefit in kind whereas a business man flying his employers aircraft for business is. What about, say, a gof pro who uses his employer's golf course of teaching and derives not only personal satisfaction but the opportunity of refining his skills? The list is endless.
I would love to hear from someone who has taken the Revenue on and won. The trouble is most of these cases are compromised - a level of understanding tends to be reached to avoid future problems, so the issue is never tested in the courts
I know this is straying off thread a little, but this idea of using something for business, but also deriving an incidental or theoretical personal benefit from it, is very similar to the requirement that all business expenses must be "Wholly & Exclusively for the purposes of the trade".
There may not be much case law about how this duality affects BIK, but there is plenty affecting the Wholly & Exclusively rule.
One that immediately springs to mind was the guy making business trips to the city, and his wife came along too. She went shopping while he visited clients. When finished his business he picked her up and drove back down the country. Revenue claimed that the trip was partly for his wife's pleasure, and not wholly & exclusively for the purpose of the trade. The courts rightly in my opinion, threw that out. There are plenty more case surrounding this area.
While not directly relating to BIK, can help to give guidance where the only benefit derived is pleasure while doing your job.
dp