Upload a file with Westminster constituency names in the first field and some numeric datum as the second field. Separate the two fields by a space. Your constituency names will be matched to those sourced from the Ordnance Survey and the map shaded to show your datum. Use Stretch values to stretch the colours in the map from 0 to the maximum value (if not 100%) in your data.
Constituencies are shaded in a colour from red to blue to represent the value from the file.