Hi My name is XXXXX XXXXX X would be happy to help with your Royal Winton (Grimwades) rooster teapot.
This is a wonderful example of 1930s Staffordshire majolica 'cottage ware'.
He should look like this, though there are often subtle differences in color depending on the individual paintress who did the decoration:
Approximately 6½" tall 9¾" from beak to tail, he has the British Design registry #810175 which confirms the design was issued in the year 1936.
It is part of the "Chanticleer" series that 'Royal Winton' (Grimwades) produced at that time that includes all sorts of rooster and hen tablewares including charming toast racks and cruet sets
and a creamer and sugar
The teapot is not quite as rare as some of the other forms but is still sought after by collectors as the crowning glory of the tea table.
If you saw your teapot for sale in an antique shop it would have a retail price of A$350. This is also the replacement value for insurance purposes.
Expect to get about 40% of this if you were to sell at auction or on line.
I do hope this helps!
Please let me know if I can be of further assistance, I would be glad to.