Impressed RD mark together with a building?- Barbican Craft Workshops

A jug with an impressed mark which is in two parts 
The capital letters RD then underneath a castle or some building?
Stands 20 cm
Thought about Bob Dawe but not the same as known marks

I wonder if it's an early mark for Rob Davies, who potted at Pantasaph Pottery in the 70s before moving to France and Germany in the 80s (it's not the monogram he was using at Pantasaph, so it's just speculation)
The letters appear to be above the Barbican Craft Workshops' Plymouth Gate mark. Several potters made slipware there in the 70s at the same time as John Pollex. I don't know when the Workshops opened; maybe the 60s?

Thanks Naomi I’ve had some of the pantasaph pottery before I’ll do some research but much obliged