Simone â€” I'm sure that your plate is Jacobean, made by Davidson for Clayton Mayers. I've had a few pieces of Davidson-made Jacobean through my hands, all superb quality like your plate, and never marked with the Reg. No. Just look at that base star â€” it shouts Davidson. Somewhere I recall reading that it dates from about 1932, possibly in Stewart & Stewart.
Some years ago I had two scarce Davidson Jacobean flower sets in stock, one in blue and the other in green, both with matching domes, together with a green Chippendale set, again with a matching dome. I put them all out at a glass fair, and by the time we had finished setting up we had sold all three!
At present, the only example of Davidson Jacobean I have in stock is a magnificent large decanter. It takes some explaining as it is pressed glass. The stopper breaks the usual rule for Jacobean & Chippendale as it has been expertly ground in. For smaller items like salad oils, a ground-in stopper is usually an indication of some modern TLC, best avoided.