One of the most solid voting blocks for Labour has historically been Roman Catholics, I can't find the data to hand but trust me it is true. So I wonder if the resignation from the cabinet of the devoutly Catholic Ruth Kelly is part of a growing alienation with the Labour party among that group.
Recent government actions of gay adoption, embryo research and a backbench attempt to loosen Northern Ireland's abortion laws have put catholics in a difficult position. With the leftist urge to find heretics rather than converts this has made Ruth Kelly a minor hate figure with the liberal left.
This antipathy towards Catholics might also explain why the Politics Home survey found that the swing towards the Tories was particularly strong in the North West.
Last week I said that Ruth Kelly was one of the only members of the government who had the ability to succeed in a field other than Labour politics. She had previously worked for the Financial Times and the Bank of England, so is clearly very able. Now she is gone the complete list of full cabinet ministers who have had any kind of career success outside of politics is..... absolutely no one (although the Attorney General, Baroness Scotland is a successful lawyer she isn't an official member of the cabinet).
This backs up my theory that the only reason the cabinet haven't rebelled against Gordon Brown yet is that they know that if they lose their cabinet positions they will never find a job of comparable stature.