Well I dont' know if the 'Way Back Machine' would help you, put in the general EH homepage address and then if you choose a date you will see the homepage as it was. If you then click EH's 'site map' in the top left corner it's probably the easiest way to see if the silbury pages are available. I had a quick look and for example you can see these pages on the hill from some point in early 2007
http://web.archive.org/web/20070108205603/www.english-heritage.org.uk/server/show/nav.8613

I think that's what it's showing anyway, you could look in more detail obviously, different dates and that. Although absence of evidence would't mean evidence of absence, it just might not have recorded the site on the day your video was there, if it was there?