In this painting of Robert Walpole by John Theodore Heins Robert is painted with a crown on his right. Robert Walpole is according to Wikipedia "a British politician who is generally regarded as the de facto first Prime Minister of Great Britain".
pictured above : Portrait of Sir Robert Walpole (1676-1745) Earl of Orford, painted by John Theodore Heins (1697-1756) followed by a close-up of the crown. attributed to Norwich Castle / Public domain
When looking at a portrait of him I noticed a crown on his right which looked odd to me since Walpole certainly wasn't royalty and the way this portrait is painted reminded me of royal portraits, like for example the portraits of his contemporaries George I and George II which use many of the same elements:
George I and George II both monarchs during Walpole's time as Prime Minister displayed in a similar way. George I - Studio of Godfrey Kneller / Public domain. George II - Thomas Hudson / Public domain
So my question is : Why did Robert Walpole get painted with a crown on his right side?
I have searched a lot on the Internet but with no avail, am I missing something obvious here or is the answer a little more nuanced?