Ah yes found it, 1802. Thanks.
http://209.85.135.104/search?q=cache:OkChLv27Z_gJ:arheologija.ff.uni-lj.si/documenta/pdf33/nash33.pdf+skinner+anglesey+tombs&hl=en&ct=clnk&cd=5&ie=UTF-8
(The link is of interest to the rest of this thread as well).

Rather than waste a good theory, I'll turn this one round and speculate that maybe Emmeline was inspired by him, not vice versa!

But equally, Merewether might have been inspired by him. He was into "speed tombrobbing" as Rhiannon calls it, digging eight of the Priddy Nine Barrows in a week in 1815. http://www.themodernantiquarian.com/site/3256/priddy_nine_barrows.html

Very interesting sam, thank you. Also to Nigel for the link to John Skinner's words -

"...he came to a mouth of a passage covered with a square stone similar to that at (nearby) Plasne-wydd, anxious to reap the fruits of his discovery he procured a light and crept forward on his hands and knees along the dreary vault, when lo! In a chamber at the further end a figure in white seemed to forbid his approach. The poor man had scarcely power sufficient to crawl backwards out of this den of spirits..."

The poem by Emmeline Fisher (1825–1864) and left in Silbury is entitled Suggested by the opening made in Silbury Hill, Aug 3rd 1849 contains the lines -

"Hark, as we move,
Runs no stern whisper through the narrow vault?
Flickers no shape across our torch-light pale,
With backward beckoning arm? No, all is still."

Very similar. Emmeline Fisher's poem can be found in full at http://megalithicpoems.blogspot.com/ (January 2008 Archives).