your point about road tax is rubbish because i doubt that estates roads are paid for by the government. it will be the residents (that guy) who pay for the roads if its anything like the similar estates around here.
Any point about road tax is rubbish, there is no such thing as road tax it was abolished in 1936.
Unadopted roads are the responsibility of the residents, you can still legally use them however. Private Roads when used for access are also perfectly legal to use.
The jerk in the Beemer sounds a right **** tbh, assuming the story is true.