I dont know how to use Python but is there a way of displaying the UK Grid reference on the layout view? My data frame has British National Grid projection.
Are you trying to display a field name for Data Driven Pages? In layout select insert then select "Dynamic Text" then "Data Driven Page Name"
Trying to use the current coordinates from British National Grid and convert to grid reference e.g SP895879 and write this automatically on my document.
Not sure if your goal is to have the grid/graticule displayed on the map, but if that is the case look at this:
A quick tour of data frame grids and the Grids and Graticules Wizard
ArcGIS Help (10.2, 10.2.1, and 10.2.2)
Chris Donohue, GISP
Retrieving data ...