It is grouting being summarily dismissed that is the big clue to what is going on here. I personally do not think that grouting as things stand is the best solution (pun unintended), but it should not be dismissed until all the facts are known. Based on the knowledge we have at present, grouting, whilst undoubtedly requiring addition holes drilled into a flank that are undesirable, is surely and obviously less of a risk than attempting to dig out the tunnels ?
My own would differ from Nigel's opinion in one respect, in that I cannot fully pin the move down to a research agenda. There are those that are rubbing their egos with glee at the prospect I suspect, but I think the majority are good honest people who simply want to do right after so many wrongs have been inflicted on Silbury by archaeologists. This is more compulsive and persuasive than gaining a name for oneself, and it is this driving the suggestion the tunnels have to be redug.
I want to stop this re-dig and would like to know if there was ultimately a collapse of the voids how much surface area would be lost and estimate regarding what archaeology could be recovered form that surface area beforehand ? Silbury could be monitored for up to ten years to see what is happening, but actually I don't see them going for it.
VBB