According to the website for the Imperial War Museum, shell failure at the Somme was a significant issue:
To make matters worse, it has been been estimated that as many as 30% of the shells failed to explode.
Similarly, shell failure was a problem at the Battle of Jutland. In that case it was Churchill who took responsibility although he did not know about the shell defects.
(from British Naval Supremacy and Anglo-American Antagonisms, 1914-1930 by Donald J. Lisio)
Despite the problems with testing and manufacturing, it was Churchill who accepted responsibility. Regarding shell use on land however, I can not find any scapegoats or anyone who faced repercussions for duds. Were there similar cases like the one referenced above, either in regards to the the Somme or the Western Front in general?