Via The Volokh Conspiracy, this is a database of the records of the Old Bailey from 1674 to 1834. It's extremely nifty in that it has a graphing tool so you can easily analyse crimes, verdicts and punishments. I used it to generate a graph of crimes involving killing by decade (all verdicts).
The results are quite interesting. Apparently the Old Bailey saw between 10 and 15 cases involving killing each year during this period. Call it one per month. I wonder how many it is now?
To get a handle on the answer to this question, I've searched the Google News archive for pleas to charges of murder in 2006 and come up with 27 stories. Some, however, are duplicates and others are not actually Old Bailey cases at all. The edited list looks like this:
I think it's fair to say that by the time you've added in the manslaughter charges (and possibly the attempted murder charges too - the definition used is not clear) the current figure will be well in excess of what we saw in previous centuries.
This all deeply unscientific of course, but interesting nevertheless.