Kaz's link is rather interesting...
Please look at the paragraphs under the heading:
Significant risk of physical harm even if the instructor was experienced.
"In assessing the likelihood that such a risk would materialise, the Court of Appeal considered the statistical evidence that one in 500 light aircraft flights in 2007 ended up in a serious accident, which meant that it could not be seen as a trivial risk." (My bolding.)
I find that statistic rather difficult to believe.