I've solved the Alexa glitch problem that I mentioned a couple of days ago.
At home, I have the official Alexa toolbar as downloaded from the Alexa site.
At work I had a custom Alexa toolbar which was supplied with some software that I installed.
It seems that the custom toolbar stopped working properly for some unknown reason, so it was returning the same rank figures that I had a few days ago.
I have now uninstalled the custom toolbar and installed the official Alexa toolbar and I get the same results in both places.
I'm pretty sure that the custom toolbars given away by other companies are purely so that if you visit their website, you have Alexa running and therefore help to increase their rank. Maybe I should create a custom toolbar and give it to my customers.