Silbury Hill 180
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Silbury Hill

Silbury updates

Doesn't look like the Confined Spaces regulations are at all applicable here -
http://www.opsi.gov.uk/SI/si1997/19971713.htm

As for Health and Safety, what's healthy and safe for the chosen invitees would be equally healthy and safe for everyone else, wouldn't it?

I think every kid in the school should put in a request in writing.....

Taking children into an old drift that has been driven into an artificial, unstable hill with a history of recent collapse would be extremely foolhardy to say the least.