NOTE: This was developed in March 2008 and the calculations are no longer accurate. They are close but not exactly right.
Update 11 August 2011: Want this as an app for your smartphone? Click here
A personal annoyance at the moment is the use of the term AA rates. It seems companies love to tell employees they pay at AA rates or charge customers at AA Rates. However due to a recent annoying experence I decided to read up on this, and to findout what the AA rate actually is.
Well imagine my surprise when I didn't find one magic overall AA rate! What I did find is there is a AA rate per vehicle, so how you get one rate is beyond me (I guess you could take the avg value of everyone in the company, but that sounds like too much work for admin/financial staff who need to update it each time someone joins/leaves).
Anyway I decided to take that and some of the Excel skills I have been taught recently and build a nice Excel speadsheet (2007 version) which works it out for you (download below). You can get the details on the rules and the fuel price (which you will need) from the AA site.