As far as I can make out,
a) nothing in the alleged amendment stops a student pilot from starting up on his own - article 26 says that if he holds a medical, is over 16 and on the authorisation of an instructor, can not only start up but of course can fly solo.
b) the ANO as currently published on the CAA's website does not include this alleged amendment to article 50
Perhaps there is loss of communication between the CAA and the AAIB. How unusual...
Really Mr AAIB, you should desist from inaccurate propaganda that only serves your views on the way it should be!
To those who think he can only start up after he has gone solo, I would ask whom you think was the commander of the aircraft on his first solo? Maybe you should read article 26 before posting?
HC