Beeley's interview is presented along with one Syrian woman's horrific report of children being kidnapped and having their organs removed. That's raw intelligence and unlikely to be picked up and explored by any Western MSM.
Believable, without further investigation, however, is Beeley's statement that these tunnels were built with slave labor. Clearly the walls of the tunnels are made by heavy equipment and not by hand so the only question is who provided the equipment and the funding? Exactly who played what role is not clear but I have not doubt that it will eventually be shown what foreign powers have been responsible for the killing and destruction in Syria.
Poor Syria has been subjected to a large-scale attack by foreign jihadi infantry and the existence of these tunnels is proof that the jihadis have substantial outside backing.