Sixth-plate, probably mid 1850s. It came to me with another image by John Urie, Glasgow, and it is in an identical case, so it is possibly connected. Sadly though no identification of sitter or photographer.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/24469639@N00">Photos of the Past</a> from Hanwell, London, UK
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/whatsthatpicture/32322077041/">Daguerreotype of a bespectacled young man reading. 1850s</a>