Grid references to lat/long values?

I've got a long list of grid references (2766 to be exact) in an excel file that I want to convert to shapefile format. I can do this with latitude and longitude values, but is there any way to do it with grid references? Alternatively is there a quick way to turn all the grid references into lat/long values? Grid references are in two different forms/accuracy levels, eg. TR37 or TR3174.

Many thanks,
James