I think we still have no idea if this is done or not. Someone call a real journalist.
That is ludicrous. Imagine your statement applied to any other scenario such as law...
Prove the person didn't commit the murder or he gets life.
It is precisely why those alleging a hypothesis must prove the thesis, it is not the job of everyone else to disprove an unproven hypothesis.
They would have to ground-penetrate the entire City of London and Greater London conurbation.
Anyway, this comment on the article you reference is interesting:
"The truth is somewhere in between, if the JCB's were mini diggers and secondhand it would make economic sense to bury the kit and not a lot of space would be lost..."
Also this quote from http://www.itv.com/news/london/2014-06-06/hundreds-of-jcb-di...:
"The diggers used are tiny little machines and they can be lifted out with a block and tackle. There is always an exit strategy for the equipment."