The UK Ordnance Survey makes available free mapping resources for use in projects under their OS OpenData licence
One of these sets of data that may be useful to people with British Ancestry is the parish boundary maps. FTAnalyzer can use this data and it is provided here under this licence. Please note this data
Contains Ordnance Survey data © Crown copyright and database right 2014
The data set is current parish boundaries and won't match exactly with historic parish boundaries as these do occasionally change. However for the most part the parish boundaries have remains as is for hundreds of years.
You can download the boundary map from here.
To install simply unzip to any directory eg: c:\Custom Maps and then in Tools | Options | Mapping Settings in FTAnalyzer set the custom maps folder to this directory. Also then tick the box to use British Parishes.