I switched from a staff variable rate to a staff fixed rate in January 2007. There was no other change in between.That MFA doesn't say whether or not you are entitled to revert to a tracker on the expiry of the Staff Fixed Mortgage.
What does the MFA that you signed in August 2006 (when you switched from your tracker) say?
Incidentally, the wording above suggests that you switched from a fixed rate mortgage to a Staff Fixed Mortgage in January 2007, whereas your earlier post suggested that you switched from a tracker to a Staff Variable Mortgage in August 2006 - did you also switch from a Staff Variable Rate to a fixed rate mortgage at some point between August 2006 and January 2007?
You have to read the original loan agreement and any subsequent MFAs together.