This is a good Mason’s ironstone large dinner plate produced at the time when Mason's was owned and controlled by George L Ashworth and Brothers after the bankruptcy of C J Mason in 1848.
This large plate is decorated in a the striking chinoiserie pattern called "Table and Flower Pot" pattern, as illustrated on Page 104 of "A Guide to Mason's Patent Ironstone Patterns" published by The Mason's Collectors' Club. The pattern would have been transfer printed then boldly hand enameled with good detail and additional hand gilding. 
The base carries a transfer printed Royal Arms Mark with Ironstone China below, together with an impressed Ashworth mark, dating this piece to circa 1875.
 
DIMENSIONS
Diameter
10.07 in
Height
1.13 in