"But he had already decided what that right solution was and that wasn't 'tunnelling', his solution that he campaigned fearlessly for (was someone threatening him?) was grouting; rather than re-filling with chalk. "

Totally, totally untrue.
Our Campaign has always been and always will be what's least damaging for Silbury, as decided by independent structural experts with no interference from anyone else or any other issue.
On Saturday for the first time ever, on the basis of acknowledged gaps in his knowledge, a proper expert told the public his opinion.
That, subject to his further consideration in the light of as much further research as can be done, is progress. About time too.