The "Eltham Coin", subject of a book by numismatist Charles Clarke, later proved to be a Peny-Yard Penny, from Henry III's reign. 
More information see: Crowther-Beynon, V. B. (1929). "<a rel="nofollow" class="external text" href="https://archive.org/details/britishnumismati2n10harr/page/n139">Some Notes on 'Peny-Yard Pence'</a>". British Numismatic Journal
<a href="https://en.wikipedia.org/wiki/Charles_Clarke_(numismatist)" class="extiw" title="en:Charles Clarke (numismatist)">Charles Clarke</a> (1719-1780)
<p><b>Originally:</b> Clarke, Charles. (1751). <i>Some Conjectures Relative to a Very Ancient Piece of Money</i>.<br></p>
<b>Immediately:</b> <a rel="nofollow" class="external text" href="http://www.mernick.org.uk/englishjettons/when.htm">When were English Jettons first recognized?</a>