This photo is from a car exhibition and thus that car has no license yet. Vaguely visible is a show plate with the BLMC logo and the word 'Limousine'. But it has the wide bootlid combined with the chrome overriders on the bumper, so it dates between mid 1975 and mid 1976.
The vinyl roof was a rarely purchased option.

Contributed from the Flickr photo hosting account of Trigger's Retro Road Tests. Used with permission.