Did your ancestor work in a post office? Mine was a "postal runner" which means she was what we now call a letter carrier. The British Postal Museum & Archives has launched a new website where you can search information on your Postie ancestors.
The area you want to search is at the top called "Collections and Catalogue"
Here on the right hand side of the screen you will find a list to search. Particular areas of interest for ancestor records are: Notable Individuals, Appointment Records, Pensions & Gratuities, and Financial Records.