The "coupe" probably refers to "drophead coupe"
I'm actually surprised at how many of these Somerset convertibles are here in Canada, I know of at least six of them in the membership roster of the British Saloon Car Club of Canada (and there must be more than that elsewhere in Canada), I don't know how common the Somerset convertible is over in England...
I have actually seen one Somerset convertible in person, near Regina, Saskatchewan, it was nearing the end of a full restoration and haven't seen it since.