BillyHayes, general secretary of the Communication Workers Union, said the development was "the best possible Christmas present for the majority of our agency members".
He said only BillyHayes - general secretary of the Communication Workers' Union, which Mr Johnson himself used to be head of - had come out in support of AV.
"While we welcome the publication of draft clauses to extend the law to private property - which is a longstanding loophole leaving thousands of dog attack victims without recourse in law - there is still no timetable for the implementation of this change, " said CWU general secretary BillyHayes.