Thank you, Roy.
Sowerby pattern 1286 (shown on page 5 of pattern book IX, 1882). I believe the registration date is indeed 29 October1877 -Parcel 9, putting it into the RD bundle 315664-674, but I'm not sure which exact one it is.
I have only seen one example before (also in purple marbled glass) - see photo.
I will try and post the pattern book picture later today.
Fred.