The issues at Thornborough are clear, that is not the case with Silbury.
What are you trying to achieve ?
Save Silbury - from who or what ?
If you want the hill to stay as it is now and nothing be done until the wider public are aware of the situation and can debate and have a say then make this clear.
If not this what do you want - do you want to stop the rebore of the tunnels - what ?