Thanks all. I knew registration was a bit relaxed in the early days but I've got a few that are missing way past the Bill. What I've read suggests a link to miscarriage and infanticide - I hope it was neither in this case.
This ancestor had four known illegitimate births, all different fathers as far as I can tell, but not one in or around 1847 (1840, 1842, 1852 and 1854) so I'm baffled. I found it in the actual criminal register but aside from the charge and the outcome, no details are given. I'll need to look for a newspaper report or other court docs.
Thank you.